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The IQ Metrics Blog

Intelligence, explained plainly

What the scores mean, how the tests work and what the research actually shows — written for a general reader, with every figure carrying the scale it was measured on.

185 articles5 topicsLast updated October 16, 2026
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Bar chart of the number of neurons in the cerebral cortex: domestic cat about 250 million, domestic pig 307 million, small mixed-breed dog 429 million and golden retriever 627 million, from counts by Kazu and colleagues (2014) and Jardim-Messeder and colleagues (2017), with the human cortex at about 16.3 billion for scale.Understanding IQ

Pig IQ

Pigs have no IQ score: no validated test gives one. Studies measure single skills instead. Four pigs acquired a joystick video task, pigs follow each other to food and read some human cues, a mirror result failed to replicate, and one pig cortex held 307 million neurons, between a cat and a dog.

11 min read
Bell curve of IQ scores with mean 100 and standard deviation 15, split at 90 and 110: 25 percent of people score below 90, 50 percent score between 90 and 110 with 100 at the centre, and 25 percent score above 110.Scores & Scales

What Does an IQ of 100 Mean?

An IQ of 100 is the exact average: the 50th percentile on the standard scale, with half of people scoring below and half above. Major test charts label it Average. See why 100 is the average, whether it is good, how many people score it and what it predicts.

9 min read
Bar chart of the number of neurons in the whole brain of five parrot species: Goffin's cockatoo 1.16 billion, grey parrot 1.57 billion, sulphur-crested cockatoo 2.12 billion, kea 2.15 billion and blue-and-yellow macaw 3.14 billion, from a 2016 count by Olkowicz and colleagues, with the human brain at 86 billion for scale.Understanding IQ

Parrot IQ

Parrots have no IQ score: no validated test gives one. Studies measure single skills instead. Alex, a grey parrot, named the number in sets of up to six items and used none for zero, kea predicted draws from odds, and parrot brains hold about twice as many neurons as primate brains of the same mass.

11 min read
Bell curve of IQ scores with mean 100 and standard deviation 15, with the area at or below 80 shaded: 9.1 percent of people score 80 or lower, of whom 2.3 percent score below 70 and 6.9 percent score 70 to 79.Scores & Scales

What Does an IQ of 80 Mean?

An IQ of 80 is the 9th percentile on the standard scale: about 1 person in 11 scores 80 or lower. Major test charts call it the bottom of the Low Average band, and the band just below it is called borderline on some. See what 80 means, how accurate it is and what it predicts.

10 min read

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IQ Scale By AgeScores & Scales

IQ Scale By Age

The IQ scale is the same at every age, with an average of 100, but the test changes: the WPPSI-IV covers ages 2.5 to 7.5, the WISC-V ages 6 to 16 and the WAIS-IV and WAIS-5 ages 16 to 90. See which test fits each age, how a child's IQ was once calculated and how stable IQ is over a lifetime.

10 min read
Bar chart of the number of neurons in the cerebral cortex: domestic cat about 250 million, domestic pig 307 million, small mixed-breed dog 429 million and golden retriever 627 million, from counts by Kazu and colleagues (2014) and Jardim-Messeder and colleagues (2017), with the human cortex at about 16.3 billion for scale.Understanding IQ

Pig IQ

Pigs have no IQ score: no validated test gives one. Studies measure single skills instead. Four pigs acquired a joystick video task, pigs follow each other to food and read some human cues, a mirror result failed to replicate, and one pig cortex held 307 million neurons, between a cat and a dog.

11 min read
Bell curve of IQ scores with mean 100 and standard deviation 15, split at 90 and 110: 25 percent of people score below 90, 50 percent score between 90 and 110 with 100 at the centre, and 25 percent score above 110.Scores & Scales

What Does an IQ of 100 Mean?

An IQ of 100 is the exact average: the 50th percentile on the standard scale, with half of people scoring below and half above. Major test charts label it Average. See why 100 is the average, whether it is good, how many people score it and what it predicts.

9 min read
Bar chart of the number of neurons in the whole brain of five parrot species: Goffin's cockatoo 1.16 billion, grey parrot 1.57 billion, sulphur-crested cockatoo 2.12 billion, kea 2.15 billion and blue-and-yellow macaw 3.14 billion, from a 2016 count by Olkowicz and colleagues, with the human brain at 86 billion for scale.Understanding IQ

Parrot IQ

Parrots have no IQ score: no validated test gives one. Studies measure single skills instead. Alex, a grey parrot, named the number in sets of up to six items and used none for zero, kea predicted draws from odds, and parrot brains hold about twice as many neurons as primate brains of the same mass.

11 min read
Bell curve of IQ scores with mean 100 and standard deviation 15, with the area at or below 80 shaded: 9.1 percent of people score 80 or lower, of whom 2.3 percent score below 70 and 6.9 percent score 70 to 79.Scores & Scales

What Does an IQ of 80 Mean?

An IQ of 80 is the 9th percentile on the standard scale: about 1 person in 11 scores 80 or lower. Major test charts call it the bottom of the Low Average band, and the band just below it is called borderline on some. See what 80 means, how accurate it is and what it predicts.

10 min read
Bar charts of neuron counts: the African elephant brain holds 257 billion neurons against 86 billion in the human brain, but the elephant cerebral cortex holds 5.6 billion against 16.3 billion in the human cortex, from a 2014 count by Herculano-Houzel and colleagues.Understanding IQ

Elephant IQ

Elephants have no IQ score: no validated test gives one. Studies measure single skills instead. One of three Asian elephants passed the mirror mark test, six waited for a partner before pulling a rope, and wild herds use name-like calls, yet one elephant's cortex held 5.6 billion neurons, a third of the human count.

10 min read
Bell curve of IQ scores with mean 100 and standard deviation 15, split at 90 and 110: 25 percent of people score 90 or lower, 50 percent score between 90 and 110 and 25 percent score 110 or higher.Scores & Scales

What Does an IQ of 90 Mean?

An IQ of 90 is the 25th percentile on the standard scale: about 1 person in 4 scores 90 or lower. Major test charts call it the bottom of the Average band, while simpler charts call it low average. See what 90 means, how accurate it is and what it predicts.

7 min read
Bar chart of cerebral cortex neuron counts: about 250 million in a domestic cat, 429 million in a small mixed-breed dog and 627 million in a golden retriever, from a 2017 count by Jardim-Messeder and colleagues.Understanding IQ

Cat IQ

Cats have no IQ: no validated test gives one. Studies measure narrower skills. Cats tell their own names from other words and follow a pointing finger as well as dogs do, but struggle with hidden-object puzzles, and a cat's cortex holds about 250 million neurons against 429 to 627 million in the dogs counted.

10 min read
Three grids of 1,000 squares showing how many people score a printed 145 or higher: 1 in 741 on the standard deviation 15 Wechsler scale, 1 in 407 on a standard deviation 16 scale and about 30 in 1,000 on the standard deviation 24 Cattell scale.Scores & Scales

What Does an IQ of 145 Mean?

An IQ of 145 is three standard deviations above average: the 99.87th percentile, roughly 1 person in 741. It is where the Stanford-Binet 5 changes its label to very gifted, but on the Cattell scale the same printed number is only the 97th percentile. See what 145 means, how rare it is and how far to trust one score.

8 min read
Bars showing the percentile a printed IQ of 115 stands for on three scales: 84.1st on the standard deviation 15 scale used by Wechsler tests, 82.6th on a standard deviation 16 scale and 73.4th on the standard deviation 24 Cattell scale.Scores & Scales

What Does an IQ of 115 Mean?

An IQ of 115 is one standard deviation above average: the 84th percentile, roughly 1 person in 6. It is High Average on the Wechsler children's scale and means the same at any age. See how accurate a single 115 is, why labels differ, and what a printed 115 means on other scales.

8 min read
A grid of 100 children with 10 dark dots, 20 lighter dots and 70 faint dots, showing that handwriting difficulties affect between 10 and 30 percent of school-aged children, with three cards: 30 gifted versus 35 typical children in a 2025 study, 101 and 102 students in two graphology tests, and no study linking messy writing to IQ.Mind & Everyday Life

Handwriting and IQ

Is bad handwriting a sign of a high IQ? We found no study that says so. Handwriting is a motor and attention skill that affects 10 to 30% of school-aged children, gifted children wrote with weaker quality in one small study, and graphology failed two direct tests. Here is the evidence.

8 min read
Bars showing correlations between personality and intelligence from two meta-analyses: openness 0.20, the activity facet of extraversion 0.23 with general mental ability, sociability 0.17 with verbal abilities, neuroticism minus 0.09 and sociability minus 0.13 with quantitative reasoning, with overall extraversion negligible.Mind & Everyday Life

Introverts and IQ

Do introverts have a higher IQ? Not in the data. Two large meta-analyses find openness is the Big Five trait most tied to IQ (rho = .20), while overall extraversion is negligible. Here are the numbers, what they mean in IQ points, and where the introvert charts come from.

7 min read
Bars showing the average full-scale IQ gain after a year in the 2004 trial: 4.3 points in the drama and no-lesson groups and 7.0 points in the keyboard and voice groups, a difference of 2.7 points, with three cards: 144 children, 54 studies in the pooled analysis and more than 10,500 twins.Research & Evidence

Music Lessons and IQ

Do music lessons raise IQ? One 2004 trial of 144 children found a 2.7-point edge, but a meta-analysis of 54 studies finds no overall effect once study quality is controlled, and a study of more than 10,500 twins finds the link vanishes within pairs. Here is the evidence.

7 min read
Bars showing odds ratios per one standard deviation lower cognitive ability in 3,258 US veterans: alcohol abuse or dependence 1.20, depression 1.32, PTSD 1.39, generalized anxiety disorder 1.43 and PTSD plus generalized anxiety disorder 2.50.Understanding IQ

PTSD and IQ

PTSD and IQ: does PTSD lower intelligence? The best evidence says lower ability before a trauma raises the risk, with the top quarter at 48% lower risk in a 2,386-twin study. After PTSD, gaps appear in verbal learning and speed. Here is what the studies show.

10 min read
Bars showing the correlation between FMRP protein level and full-scale deviation IQ in fragile X syndrome: 0.73 across all 143 people, 0.45 in 44 females, 0.22 in 99 males and below 0.06 in 66 fully methylated full-mutation males.Understanding IQ

Fragile X and IQ

Fragile X and IQ: fully methylated full-mutation males are described as moderate to severe intellectual disability, while females vary widely. A 2024 study of 143 people found a near-normal IQ curve shifted down, and FMRP protein level mattered except in fully methylated males.

9 min read
Bars showing anxiety in 45 children with Williams syndrome followed over time: 60 percent had an anxiety diagnosis at the first assessment, 82.2 percent at some point in the study and 51.1 percent had chronic, persistent anxiety.Understanding IQ

Williams Syndrome and IQ

Williams syndrome and IQ: mean full-scale IQ was 61 in 62 adults, and 292 children averaged in the borderline range on the KBIT-2, stable from age 4 to 17. Language is a relative strength and visuospatial construction an extreme weakness. Here is what the studies show.

9 min read
Bars showing how much lower the risk of death from each cause was per one standard deviation higher childhood intelligence in 65,765 Scots followed for 68 years: respiratory disease 28 percent, coronary heart disease 25 percent, stroke 24 percent, injury 19 percent, dementia 16 percent and cancers not related to smoking 4 percent.Understanding IQ

Do Smart People Live Longer?

Do smart people live longer? On average, modestly: 16 studies of 1,107,022 people found a 24% lower risk of death per standard deviation of early-life intelligence. In 65,765 Scots the link was strongest for respiratory disease, heart disease and stroke. Here are the numbers.

7 min read
Bars showing how far below healthy comparison groups people with schizophrenia score, in standard deviations: 0.43 for IQ before onset in 12 population-based studies, about 0.5 in an 18-study review, a grand mean of 0.98 across cognitive measures and 1.57 for digit symbol coding, a speed task.Understanding IQ

Schizophrenia and IQ

Do people with schizophrenia have a lower IQ? On average slightly: about half a standard deviation before onset, and risk rises 3.7% per IQ point lower. But 31% of one first-episode sample kept an average or high IQ. Here is what changes before and after onset, and why speed shows the biggest gap.

12 min read
Bars with the original marshmallow studies set to 100: a 2018 replication found the link between waiting time at age 4 and achievement at 15 was half the size (50), and about 17 after controls for family background, early cognitive ability and the home environment, by our arithmetic from the reported ratios.Research & Evidence

Marshmallow Test

What does the marshmallow test really predict? The original studies linked waiting to teenage success, but a larger replication found the link half as strong and two thirds smaller after controls, and a 2024 follow-up found no reliable adult prediction. Here is the evidence, the IQ link and the trust factor.

9 min read
Three finding cards on intelligence and loneliness: loneliness affects 1 in 6 people worldwide (WHO 2025); more frequent socializing with friends went with higher life satisfaction but the link reversed among the extremely intelligent (Li and Kanazawa 2016); and in the Lothian Birth Cohort 1936, better cognitive ability at 73 went with smaller rises in loneliness by 76 (Okely and Deary 2019).Mind & Everyday Life

Are Smart People Lonely?

Are smart people lonely? No study shows a high IQ causes loneliness. One survey found friends added less to life satisfaction for the extremely intelligent, while older adults with lower ability became slightly lonelier. Here is the evidence on loneliness, gifted children and why the idea feels true.

8 min read
Bars showing global cognitive function in 613 children followed from the diagnosis of epilepsy: 73.6 percent within the normal range, 5.1 percent borderline, 10.8 percent with intellectual disability and 10.6 percent severely impaired or unclassified.Understanding IQ

Epilepsy and IQ

Does epilepsy lower IQ? Not in most children: in a 613-child cohort, 73.6% had normal cognition and about 1 in 4 did not. Early onset, a known cause and continuing treatment predicted lower scores, and valproate in pregnancy went with an age-6 IQ of 97. Here is what the studies show.

7 min read
Bars showing how much the odds or hazard of an anxiety-type disorder rise for each 15 points lower IQ: generalized anxiety disorder 1.43 and post-traumatic stress disorder 1.39 among 3,258 US veterans, and 1.51 for hospital admission with a neurotic disorder among 1,049,663 Swedish men, measured against a no-difference line at 1.0.Mind & Everyday Life

Anxiety and IQ

Does anxiety lower IQ, or do smart people worry more? Large cohorts link a lower IQ to more anxiety disorders, Mensa surveys report the reverse, and anxiety weakens working memory on test day. Here is what each study measured and where selection bias may explain the gap.

9 min read
Three findings on OCD and IQ as cards: a 2018 meta-analysis of 98 studies found slightly lower IQ than comparison groups with average scores still in the normal range; a 2020 meta-analysis reported OCD samples 3.74 points lower; and a 2025 study of 341 teenagers found mild symptoms linked to higher IQ than none or severe symptoms, an inverted U.Mind & Everyday Life

OCD and IQ

Is OCD a sign of high intelligence? A 2018 meta-analysis of 98 studies found people with obsessive-compulsive disorder score slightly lower than comparison groups, though still in the normal range. Here is what slows the scores, and where the high-IQ idea may come from.

7 min read
Bars from the Havana Survey of 11,652 children in grades 2 to 9, showing how the definition changes the share counted: developmental dyscalculia (a defective sense of numerosity) 3.4 percent, basic numerical deficits 4.54 percent and arithmetical dysfluency 9.35 percent.Understanding IQ

Dyscalculia and IQ

Can you have dyscalculia and a high IQ? Yes: it is a specific difficulty with numbers, not a low-IQ condition. Estimates of how common it is run from 3.4% to over 9% depending on the definition. Here is what the studies say, how it is assessed and how it differs from maths anxiety.

8 min read
Bars showing three estimates of intellectual disability in cerebral palsy: about 50 percent (1 in 2) in a 2012 systematic review of population-based studies, 45 percent of 1,141 people on an Australian register, and 38 percent of 21 children with hemiplegic cerebral palsy in Stockholm; the remainder in each group did not have an intellectual disability.Understanding IQ

Cerebral Palsy and IQ

What is the IQ of someone with cerebral palsy? There is no single level: about 1 in 2 children has an intellectual disability and about half do not. Here is how common it is, what predicts lower scores, why testing is hard, and why the headline figure may overstate it.

8 min read
The Big Five personality traits drawn as five spectrums, each with its three BFI-2 facets: openness (intellectual curiosity, aesthetic sensitivity, creative imagination), from conventional to curious; conscientiousness (organization, productiveness, responsibility), from spontaneous to organized; extraversion (sociability, assertiveness, energy level), from reserved to outgoing; agreeableness (compassion, respectfulness, trust), from blunt to warm; neuroticism (anxiety, depression, emotional volatility), from calm to anxious.Mind & Everyday Life

Big Five Personality Traits

The Big Five personality traits are openness, conscientiousness, extraversion, agreeableness and neuroticism: five spectrums that came out of decades of research on the words people use to describe each other. Here is what each trait means, how it is measured, what it predicts and how it changes.

10 min read
The DISC model drawn as a circle with four quadrants. Top left, D for Dominance: driven, strong-willed, forceful. Top right, i for Influence: sociable, lively, talkative. Bottom right, S for Steadiness: considerate, patient, soft-hearted. Bottom left, C for Conscientiousness: analytical, reserved, unemotional. The vertical axis runs from fast-paced at the top to moderate-paced and cautious at the bottom; the horizontal axis from questioning and skeptical on the left to accepting and warm on the right.Mind & Everyday Life

DISC Personality Model

DISC sorts workplace behavior into four styles: Dominance, Influence, Steadiness and Conscientiousness. It began with a 1928 book by William Moulton Marston and became a family of training questionnaires. Here is how the model works, what the evidence says, and why it is not a hiring test.

8 min read
A range chart of how far people with depression score below healthy comparison groups on cognitive tasks, in standard deviations with an IQ-style point equivalent. Executive function, memory and attention during an episode: 0.34 to 0.65 standard deviations, roughly 5 to 10 points on a scale with a standard deviation of 15 (Rock 2014). Executive function and attention in remission: 0.52 to 0.61, roughly 8 to 9 points (Rock 2014). Executive-function tests across 113 studies: 0.32 to 0.97, roughly 5 to 15 points (Snyder 2013). These are scores on specific tasks, not full-scale IQ.Mind & Everyday Life

Depression and IQ

Does depression lower IQ? It lowers performance on attention, memory, speed and planning tasks while an episode lasts, and some executive and attention differences remain after recovery. A permanent loss of intelligence is not shown, and two large cohorts suggest the arrow also runs the other way.

9 min read
A bar chart of how far below comparison groups people with bipolar disorder score on cognitive measures, in standard deviations with an IQ-style point equivalent. Before onset, measured ahead of time: 0.03, about half a point and not statistically significant (Trotta 2015). Before onset, estimated afterward: 0.15, about 2 points (Trotta 2015). Estimated premorbid IQ in studies of people between episodes: 0.24, about 4 points (Swidzinski 2025). After onset, global cognition: 0.62, about 9 points (Trotta 2015). Between episodes, general cognitive functioning: 0.58, about 9 points (Swidzinski 2025). Differences are small or absent before the illness and moderate after it.Mind & Everyday Life

Bipolar Disorder and IQ

Are bipolar people smarter? Not on average, but the evidence is more interesting than yes or no. Swedish data on a million men show a reversed-J pattern, excellent school grades carried nearly four times the risk in males, and after diagnosis cognitive scores run about 0.6 standard deviations lower.

10 min read
A bar chart of the typical gap, in IQ points, between the scores of two people by how they are related, calculated from the average IQ correlation for each pair (Bouchard and McGue 1981) and a standard deviation of 15. Identical twins reared together (correlation .86): about 6 points. Fraternal twins (.60): about 11. Full siblings reared together (.47): about 12. Unrelated people (no correlation): about 17. Full siblings are much closer to strangers than to identical twins. The gaps are our calculation.Understanding IQ

Do Siblings Have Similar IQs?

Do siblings have similar IQs? Somewhat. Across 69 correlations the average is .47, so two full siblings typically differ by about 12 IQ points, and about one pair in five differs by 20 or more. See the odds of every gap, what to expect from the sibling of a high scorer, and what pushes siblings apart.

8 min read
A bar chart of the correlation between humor production ability, the judged funniness of cartoon captions, and two intelligence measures in 400 students (Greengross and Miller 2011). Everyone: vocabulary .38, matrix reasoning .25. Men: vocabulary .44, matrix reasoning .27. Women: vocabulary .31, matrix reasoning .24. All six are statistically significant, and in the full sample vocabulary correlates more strongly with humor than matrix reasoning does.Mind & Everyday Life

Humor and IQ

Are funny people smarter? In student studies, the ability to write funny captions correlates about .25 with abstract reasoning and .38 with vocabulary. That is a real but moderate link: a high scorer is somewhat more likely to be funny on demand, but IQ cannot identify funny people. See the odds, the evidence and its limits.

8 min read
A range chart of how many students are identified as both gifted and disabled. Students with a disability in all US public schools: 15 percent (National Center for Education Statistics, 2024). Students identified as both gifted and in special education or a Section 504 plan, across 23 states that reported: from 0 percent to 18.66 percent, with all but two states below 10 percent (NAGC state of the states, 2022-23). The gap suggests twice-exceptional students are underidentified.Understanding IQ

Twice Exceptional (2e)

Twice exceptional (2e) means gifted and disabled at the same time, such as high reasoning with dyslexia, ADHD or autism. See the research definition, how one IQ score can hide the pattern, how students are identified and what 2026 data show about how many are found.

10 min read
A bar chart of pooled effect sizes (Hedges g) from a 2022 meta-analysis of 45 randomized trials of mindfulness-based programs in adults. Working memory: 0.23. Executive function: 0.15. All cognitive outcomes pooled: 0.15. Against active comparison groups: no significant benefit. On an IQ scale an effect size of 1.0 would be 15 points; these are averages across cognitive tests, not IQ scores.Research & Evidence

Meditation and IQ

Does meditation increase IQ? The best reviews find small gains in working memory and executive function, not in IQ, and no benefit over an active comparison. See the adult and child meta-analyses, the famous two-week study, the Transcendental Meditation claims and the brain-imaging trial.

8 min read
A bar chart of average FAS verbal fluency scores, total words in one minute for each of the letters F, A and S, among Brazilian adults aged 60 to 69 by years of schooling (Machado et al., 2009). 1 to 3 years of education: 18.3 words (14 people). 4 to 7 years: 26.1 (31 people). 8 to 11 years: 31.9 (36 people). 12 or more years: 38.7 (54 people). Education moves the score by more than 20 words.Taking a Test

Verbal Fluency Test

A verbal fluency test asks you to name as many words as you can in 60 seconds, by letter (F-A-S) or category (animals). See how it is scored, why education can move the score by about 20 words, what the task really measures and what a low count can and cannot tell you.

9 min read
A score strip from 0 to 30 for the Montreal Cognitive Assessment. The publisher's ranges are severe 0 to 9, moderate 10 to 17, mild 18 to 25 and normal 26 to 30. Markers show the original cut-off of 26, the cut-off of 23 favored by a 2018 meta-analysis, and the average score of 24.7 among 2,637 cognitively unimpaired adults in the Framingham Heart Study (2026). Many healthy older adults fall below 26.Scores & Scales

MoCA Score

A MoCA score is a number out of 30 from a 10-minute screen for mild cognitive impairment. See the four publisher score bands, why the 26 cut-off flags many healthy adults, what changes the score, what to do with a result and why a MoCA is not an IQ.

7 min read
Three finding cards about executive function and IQ from Friedman and colleagues' 2006 study of young adults. Updating, replacing what you hold in mind: highly correlated with fluid and crystallized intelligence and with WAIS IQ, a strong link. Inhibiting, holding back the automatic answer: a small, not significant relation to intelligence once the three functions were modeled together, a weak link. Shifting, switching between rules or tasks: a small, not significant relation, a weak link.Understanding IQ

Executive Function vs IQ

Executive function and IQ overlap but are not the same thing. Of the three executive functions, only updating working memory was highly correlated with intelligence in one study of young adults. See the three functions, a twin study, how reliable the tasks are and why training claims fall short.

8 min read
A bar chart of standardized associations with gait speed in 904 adults aged 45 in the Dunedin study, adjusted for sex. Full-scale IQ at 45 measured with the WAIS-IV: 0.38. Grip strength: 0.36. Chair-stand test: 0.34. Neurocognitive health at age 3: 0.26. Total brain volume: 0.15. Cortical thickness: 0.09. These are associations, not proof of cause.Research & Evidence

Walking Speed and IQ

Walking speed and IQ are linked: in 904 adults aged 45, higher full-scale IQ went with faster walking (0.38). See what else went with gait speed, why childhood brain health at age 3 mattered, what walking speed predicts in older adults and why it is a health marker, not an IQ test.

7 min read
A bar chart of effect sizes, Cohen's d, from published meta-analyses of head injury and cognitive scores. Mild traumatic brain injury, delayed memory in the first 3 months: 1.03. Moderate-severe injury across all follow-up periods: 0.74. Mild injury, all domains pooled: 0.54. Mild head injury across all follow-up periods: 0.24. Two or more concussions versus one in athletes: 0.06. Mild injury after 3 months in unselected or prospective samples: 0.04. On an IQ scale, d of 1.0 is 15 points; these are averages across cognitive tests, not IQ scores.Research & Evidence

Can a Concussion Lower Your IQ?

Can a concussion lower your IQ? Meta-analyses of mild and severe head injury show scores dip in the first days, recover within weeks for most people and stay lower after moderate or severe injury. See the effect sizes in IQ points, why clinic samples look worse and why a baseline is rarely available.

8 min read
Three cards about the KBIT-2. Three subtests, three scores: Verbal Knowledge and Riddles plus Matrices, for ages 4 to 90, in about 20 minutes, giving Verbal, Nonverbal and IQ Composite standard scores with a mean of 100 and a standard deviation of 15. Revised in 2022: the revision uses norms from 2021 data, while the first edition used data collected in 2002 to 2003. Agreement with longer tests: Pearson reports a correlation of .77 between the revised IQ Composite and the KABC-II NU, and an independent study of 101 children found .72 with the WISC-V but wide error in predicting individual scores.Scores & Scales

KBIT-2 Test

The KBIT-2 is a 20-minute IQ screen for ages 4 to 90 with three subtests: Verbal Knowledge, Riddles and Matrices. See how its scores work, what the 2022 KBIT-2 Revised changed, how closely it matches the WISC-V and KABC-II, and why it is a screen rather than a full evaluation.

8 min read
A chart of stated testing times in minutes. The WASI-II runs 15 to 30, the KBIT-2 about 20, the CCAT 15, the Wonderlic cognitive section 12, Raven's Standard Progressive Matrices 20 to 45, the WPPSI-IV 30 to 60, the WAIS-5 45 to 60, the WAIS-IV 60 to 90 and Mensa admission sessions 60 to 135 minutes.Taking a Test

How Long Does an IQ Test Take?

An official IQ test usually takes 45 to 90 minutes of testing: 45 for the WAIS-5, 60 to 90 for the WAIS-IV, 12 for the Wonderlic. See the time for every major test, how many questions to expect, why two people take different amounts of time and what a full evaluation adds.

10 min read
Three cards summarize an official IQ test. Supervised group test: American Mensa lists $60 for local group testing and $99 for private testing at approved testing facilities, and Mensa UK lists 49 pounds. University training clinic assessment: fees run from $300 at the University of Nevada, Reno to $2,500 at the University of Victoria. Testing time: Pearson lists 45 minutes for the seven-subtest WAIS-5 FSIQ and 60 minutes for the ten primary subtests.Taking a Test

Official IQ Test

There is no single official IQ test: official means a standardized test given by a qualified psychologist or a supervised exam such as Mensa's. See how long it takes, what it costs (from $60 to $2,500), where to book one and what score you actually get.

11 min read
A bar chart shows average digit span in one University of York study. Native Mandarin speakers recalled 8.84 digits in Mandarin, native English speakers recalled 6.94 digits in English, and the same Mandarin speakers recalled 5.77 digits in English. Each group had 36 students.Scores & Scales

Digit Span Test

A digit span test asks you to repeat lists of digits; on the WAIS it has three tasks of eight items. Verified adult averages run from 5.3 to 6.9 digits, not seven, and language matters: 8.84 in Mandarin versus 5.77 in English for the same people.

14 min read
A bar chart of average simple reaction time in milliseconds from six instruments. A falling rod gave 203 in college football players, a calibrated computer 213 after removing hardware delay and 231 as recorded, a computerized test in the same football players 268, the Human Benchmark online median 273 and a keypad device 290 at age 30.Understanding IQ

Reaction Time Test

A reaction time test depends on the equipment: 203 ms with a falling rod, 231 ms on a calibrated computer, 273 ms online. See the ruler drop conversion table, why online scores run slow, driving and sprint reaction times, and what really changes your speed.

12 min read
A bar chart draws the 1916 classification of Lewis Terman on an IQ scale from 0 to 150. The three retired labels are highlighted: idiot below 20 or 25, imbecile 20 or 25 to 50 and moron 50 to 70, with adult mental levels of up to about 3, 3 to 7 and about 7 to 11 years. The other bands run from border-line deficiency at 70 to 80 up to near genius above 140.Scores & Scales

What IQ Is a Moron?

In the old clinical scheme a moron had an IQ of roughly 50 to 70, an imbecile about 20 or 25 to 50 and an idiot below that, according to Lewis Terman in 1916. See who coined the words, how the cut-offs moved, what the 1913 UK Act said and why the labels were dropped.

11 min read
Three cards compare correlations. Grit and school achievement: a weighted correlation of .19 across 137 studies and 285,331 people. Grit and conscientiousness: a corrected correlation of .84 across 88 samples and 66,807 people. Intelligence and school grades: a corrected correlation of .54 across 240 samples and 105,185 people, corrected for range restriction, so not like for like with the grit figures.Understanding IQ

Grit vs IQ

Grit is weakly to moderately linked to school achievement and overlaps almost completely with conscientiousness. See what the original grit studies, two large meta-analyses, the marshmallow test and a retracted test-motivation paper really show about grit vs IQ.

10 min read
A bar chart shows four measured IQ gains from adoption, each against a different comparison group: 3.18 points in a Swedish half-sibling comparison, 4.41 points in a Swedish full-sibling comparison, 7.7 points for neglected French children adopted into lower-SES homes and 19.5 points for those adopted into higher-SES homes.Research & Evidence

Adoption and IQ

Adoption can raise average IQ by about 3 to 4 points in a large Swedish sibling study and by 8 to 20 in a French study of neglected children, yet adoptees come to resemble their birth parents. See what adoption and twin studies show, and what they cannot.

12 min read
Three cards summarise dyslexia and IQ. No IQ threshold: the UK Rose Review says dyslexia occurs across the range of intellectual abilities, and US states may not require an IQ-reading gap. An uneven profile: in Pearson WISC-V data for 24 children with a reading disorder, working memory averaged 89.8 against 106.6 in matched controls. Genes: a 2022 study of 51,800 self-reported cases found 42 loci.Understanding IQ

Dyslexia and IQ

Dyslexia is a reading and spelling difficulty that occurs at every level of IQ, and the IQ-gap rule was dropped as a US requirement in 2004 and from the IDA definition in 2025. See what IQ tests show for readers with dyslexia, and what the genetics and myths add.

12 min read
A single card shows the OLSAT at a glance: seven levels, A through G, spanning kindergarten through grade 12, five reasoning clusters, and a School Ability Index scaled to a mean of 100 and a standard deviation of 16, wider than the Wechsler and Stanford-Binet 5 scale of 15.Scores & Scales

OLSAT Test

The OLSAT test (Otis-Lennon School Ability Test) is a group-administered reasoning test scored on a School Ability Index with mean 100 and SD 16, best known for New York City Gifted and Talented admissions. See how it works, its history, and the NYC admissions cutoffs and controversy.

8 min read
A comparison card contrasts PISA and an individual IQ test. PISA surveys a sample of 15-year-olds in each country and school system, reports no individual score, and rotates test booklets. An IQ test is given one to one and reports one diagnostic score to the person tested.Understanding IQ

PISA Test vs IQ Test

Is PISA an IQ test? No. PISA surveys applied school literacy across whole education systems and returns no individual score, while an IQ test diagnoses one person. See the new PISA 2025 results, published September 2026, and the real debate over using PISA as a national IQ proxy.

7 min read
A diagram shows two arrows between education and myopia. A Mendelian-randomisation study found a causal arrow from more years of education to more myopia, about a quarter of a diopter per year, but found no significant effect running the other way, from myopia to educational attainment.Research & Evidence

Myopia and IQ

Myopia and IQ: are nearsighted people really smarter? A 2018 genetic study of 68,000 people found the causal arrow runs from more education to more myopia, not the other way around. See the historical studies, the genetics behind the link, and why time outdoors helps.

7 min read
A line chart plots creative achievement against IQ score. The classic threshold claim draws a flat line above IQ 120. The largest meta-analysis instead finds a similar, modest correlation below and above 120, with no significant break at that point.Understanding IQ

Creativity and IQ

Creativity and IQ correlate only weakly. The largest meta-analysis ever run on the question, covering 45,880 people, found no significant threshold at IQ 120, just a modest overall link of about .17 to .25. See what the strongest evidence shows, and why the classic claim does not hold up.

8 min read
Four bars show cognitive-test gaps after COVID-19 compared with people who had none: about 3.5 IQ points when symptoms had resolved, in under 4 weeks or after 12 weeks or more, 6.3 when symptoms were unresolved after 12 weeks, and 9.5 after intensive care. The tasks were a cognitive battery, not an IQ test.Research & Evidence

Does COVID Lower IQ?

Does COVID lower IQ? The largest study found a cognitive-test gap of about 3 IQ points after resolved COVID, 6 with unresolved symptoms and 9 after intensive care. See what that measures, what other studies add, and why it is not an IQ test.

9 min read
Two rows of 23 boxes show that each parent hands on the same 22 numbered chromosomes plus one sex chromosome. The X chromosome is about 5% of the genome and holds about 15% of known intellectual disability genes, yet mothers and fathers resemble their children in IQ equally.Research & Evidence

Is Intelligence Inherited From Mother or Father?

Is intelligence inherited from mother or father? From both. A review of 111 family studies found mothers and fathers resemble their children in IQ equally (.41 each). See where the X-chromosome claim came from, why it fails, and how much IQ parents pass on.

10 min read
A grid of the ten Stanford-Binet subtests: five factors (fluid reasoning, knowledge, quantitative reasoning, visual-spatial processing and working memory), each measured once with nonverbal tasks and once with verbal tasks.Scores & Scales

Stanford-Binet IQ Test

The Stanford-Binet IQ test (SB5) covers ages 2 to 85+ with ten subtests, a mean of 100 and SD 15. See its history, how scores and labels work, why older forms used SD 16, how it differs from the Wechsler tests and which societies accept it.

10 min read
Two panels show the WPPSI-IV age bands. Ages 2 years 6 months to 3 years 11 months get three index scores (verbal comprehension, visual spatial, working memory); ages 4 years to 7 years 7 months get five (adding fluid reasoning and processing speed). Each band also gets a Full Scale IQ.Scores & Scales

WPPSI-IV Test

The WPPSI-IV test covers ages 2:6 to 7:7 in two bands, with 15 subtests, five index scores and a Full Scale IQ. See what each subtest asks, how a published sample report reads, how the score labels work, and what a preschool score can and cannot tell parents.

10 min read
Three rows comparing early scores: Bayley-4 development scales for ages 1 to 42 months are not an IQ, looking-time tasks predict later IQ with a correlation of about .36, and the first norm-referenced IQ score is available from 2 years 6 months.Understanding IQ

Baby IQ Test

No test can give a baby an IQ. Bayley scores describe development, not intelligence, looking-time tasks predict later IQ only modestly (r = .36), and real IQ scoring starts at 2 years 6 months. See what each early score means.

8 min read
Stacked bar of CDC 2022 data for 8-year-olds with autism and an IQ score on record: 39.6 percent with IQ 70 or below, 24.2 percent with IQ 71 to 85 and 36.1 percent above 85, with IQ on record for 61.4 percent of children.Understanding IQ

Autism and IQ

About 40% of 8-year-olds with autism and an IQ score on record had an IQ of 70 or below, and 36% scored above 85. See the CDC figures and their caveats, the Raven's gap of 30 percentile points, and what an IQ number cannot tell you.

7 min read
Three studies of ADHD and IQ: a 2004 meta-analysis with a gap of about 9 points, a 2006 meta-analysis of adults with a small difference, and a 2025 WISC-IV study where the gap sits in working memory and processing speed.Understanding IQ

ADHD and IQ

ADHD lowers average IQ scores by about 9 points across pooled studies, but the gap sits in working memory and processing speed, not reasoning, and the groups overlap heavily. See the meta-analyses, the index profile and what an IQ test cannot diagnose.

7 min read
Three rows on the Woodcock-Johnson V: 20 cognitive tests and 26 achievement tests on shared norms, a norm sample of 5,837 people aged 3 to 90 and older tested in 2022 and 2023, and fully digital administration by a trained examiner.Scores & Scales

Woodcock-Johnson IQ Test

The Woodcock-Johnson V has 20 cognitive tests, 26 achievement tests on the same norms, and a GIA score with an SD of 15. See what each cluster measures, why the same score can carry different labels on different reports, and how it differs from the WISC-V and WAIS.

7 min read
Three rows converting ratio IQ scores of 50, 70 and 85 to mental ages of 8.0, 11.2 and 13.6 years using an adult ceiling of 16 years, with a note that this is a convention and not a description of a person.Scores & Scales

IQ and Mental Age

Mental age is the age a typical child scores like, and ratio IQ divides it by real age. See an IQ to mental age chart from IQ 30 to 100, worked examples, and why modern tests dropped the idea for adults.

8 min read
Horizontal bars of seven test scores for Koko the gorilla from 1975 and 1976, from 71.0 on the Wechsler preschool scale to 91.7 on the Stanford-Binet, all below the human average of 100.Research & Evidence

Gorilla IQ

Gorillas have no IQ. The quoted 70 to 95 comes from tests given to one gorilla, Koko, by her trainer. See her real scores, what wild gorillas have been shown to do, and why brain size alone cannot rank animals.

8 min read
Bars showing correlations between four music-taste styles and a verbal test score: plus 0.19 for reflective and complex, plus 0.19 for intense and rebellious, minus 0.18 for upbeat and conventional and minus 0.01 (not significant) for energetic and rhythmic, from 118 students.Research & Evidence

Music Taste and IQ

Music taste and IQ are linked only weakly: the best-known study found a correlation of 0.19 with verbal ability, from 118 students. See which genres showed what, what 2026 listening data adds, and why a playlist cannot reveal IQ.

7 min read
Three cards summarising peer-reviewed dolphin findings: two bottlenose dolphins using a mirror, signature whistles working like names in wild dolphins, and sponge tool use passed down one matriline in Shark Bay.Research & Evidence

Dolphin IQ

Dolphins have no IQ, but they have passed a mirror test, use signature whistles like names and pass tool use down the female line. See the evidence, the brain data, and the peer-reviewed sceptics who question the hype.

7 min read
A bell curve for IQ scores from 55 to 175 with the top sliver above 150 shaded gold, showing 150 at the 99.96th percentile, about one person in 2,331.Scores & Scales

What an IQ of 150 Means

An IQ of 150 is about 1 person in 2,331 on a standard deviation 15 scale, the 99.96th percentile. See how rare it really is, what "genius" cutoffs actually mean, and why scores this high need a real test to trust.

6 min read
Three rows comparing the SAT correlation with general cognitive ability at 0.86 against the GRE predictive validity of about 0.33 and the LSAT predictive validity of about 0.4, with a note that these measure different things.Taking a Test

GRE and LSAT Scores to IQ

There is no official GRE-to-IQ or LSAT-to-IQ conversion. See what the SAT research actually found, what the GRE and LSAT predict instead, and why online conversion calculators have no scientific basis.

6 min read
Three rows on alcohol and cognition: a 2022 UK Biobank study linking more than seven units a week to higher brain iron and worse cognitive function, the older contested claim that moderate drinking protects the brain, and a 2025 re-analysis finding no protective effect once income and cultural factors are controlled.Research & Evidence

IQ and Alcohol

Heavy drinking clearly harms cognition; moderate drinking is genuinely contested. See what a 2022 UK Biobank study found, why older research claimed a protective effect, and why newer reviews are walking that back.

6 min read
Three rows showing the cognitive ability and BMI link shrinks from a 0.95 kg/m2 difference between families to a statistically insignificant 0.06 kg/m2 within families of siblings, a roughly 90 percent reduction.Research & Evidence

IQ and BMI

Cognitive ability and adult BMI correlate, but a sibling-comparison study found the link shrinks by about 90 percent within families. See what that implies about family background versus a direct causal effect.

6 min read
A bell curve for IQ scores from 55 to 145 with the top 5 percent above 125 shaded gold, showing 125 at the 95th percentile, about one person in 21.Scores & Scales

What an IQ of 125 Means

An IQ of 125 is about 1 person in 21 on a standard deviation 15 scale, the 95th percentile and one band below most gifted cutoffs. See how rare it is, what "Superior" means, how accurate a single score is, and what it predicts.

6 min read
Four comparison bars for cognitive screening tools: MoCA sensitivity 90 percent and specificity 87 percent versus MMSE sensitivity 78 percent and specificity 77 percent for detecting mild cognitive impairment.Taking a Test

Can an IQ Test Detect Dementia?

A standard IQ test cannot diagnose dementia; it has no personal baseline and was not built to screen for decline. How the MMSE and the more sensitive MoCA compare, why a normal score can hide early decline, and what actually helps catch it.

6 min read
Three comparison rows showing IQ and happiness correlate close to zero for individual people but show a stronger correlation between countries average IQ and average happiness, which reflects national wealth rather than individual differences.Research & Evidence

IQ and Happiness

IQ and happiness are almost unrelated at the individual level, though smarter countries do report higher average happiness. What the research actually finds, why national comparisons mislead, and what predicts happiness better than IQ.

6 min read
Three rows showing the height and IQ correlation is small, about 0.1 to 0.2 in the population and 0.08 to 0.3 in genetic correlation from twin studies, explaining only about 1 to 4 percent of the variation between people.Research & Evidence

Height and IQ

Height and IQ correlate at about 0.1 to 0.2, a real but small link. What twin studies say about where it comes from, how much is childhood nutrition, and why it means nothing for judging any one person.

6 min read
Three horizontal bars showing how rare an IQ of 160 is on three scales: about 1 in 31,600 on a standard deviation 15 scale, 1 in 11,300 on a standard deviation 16 scale and 1 in 161 on the Cattell standard deviation 24 scale.Scores & Scales

What an IQ of 160 Means

An IQ of 160 is about 1 person in 31,600 on a standard deviation 15 scale, but only 1 in 161 on the Cattell scale. What a 160 means on each scale, which tests can print one, how accurate it is, what it predicts and where the claims come from.

8 min read
Two panels comparing chimpanzees with 2.5-year-old children on the same 16-task battery: on physical tasks chimpanzees and children were each right on about 68% of trials, while on social tasks children scored about 74% against 33 to 36% for the two ape species.Understanding IQ

Chimpanzee IQ

Chimpanzees have no IQ, but they have been tested. How chimps and 2.5-year-old children scored on the same 16 tasks, what a chimpanzee brain holds, the memory claim that did not survive practice, and whether chimps have a g factor.

8 min read
A diagram of an octopus nervous system: a central circle for the brain and optic lobes holding about 200 million of roughly 500 million neurons, surrounded by eight arm circles holding about 300 million between them, or about 37 million each.Understanding IQ

Octopus IQ

An octopus has no IQ, but it has about 500 million neurons, most of them in its arms. The neuron count, the tool-use and recognition studies, why short lives leave no room for teaching, and why UK law now treats octopuses as sentient.

7 min read
An IQ axis from 55 to 145 with four bars: intellectual disability at about 70 or below plus adaptive difficulties, borderline functioning from 71 to 84, a low score below 85, and a specific learning disorder that spans the whole range.Understanding IQ

Low IQ vs Learning Disability

A low IQ, an intellectual disability and a specific learning disability are three different things, and the UK uses "learning disability" for the second. What each requires, how each is assessed, the US and UK terms, and what to do if you are worried.

8 min read
Two almost identical IQ bell curves, one for a more religious group (average 97.9) and one for a less religious group (average 102.1), overlapping by about 89 percent, drawn from a correlation of -0.14.Research & Evidence

IQ and Religion

Three meta-analyses agree: higher IQ goes with slightly weaker religious belief, r about -0.14 to -0.17, or four to five IQ points, with heavy overlap. What the numbers mean, what explains them, where they weaken and what they cannot show.

11 min read
Bar chart of six water-displacement tasks: New Caledonian crows chose the working option 76 to 89 percent of the time on four tasks but stayed near chance on the narrow-tube and U-tube tasks.Understanding IQ

Crow and Raven IQ

A crow has no IQ, but tests show what corvids can do: bend wire, plan hours ahead, count their own calls. The 7-year-old comparison traces to one 2014 study of six crows, who were at chance on two of six puzzles.

10 min read
A grid of 100 dots showing one gold dot for the person in a hundred who scores 135 or higher, one navy dot for the 130 to 134 band and 98 grey dots, beside the figures 99th percentile and 1 in 102.Scores & Scales

What an IQ of 135 Means

An IQ of 135 is the 99th percentile: one person in 102 on the Wechsler scale, but only 1 in 14 on the Cattell scale. Rarity of every score from 130 to 139, the cut-off Terman really used, how precise a 135 is, and what it predicts.

11 min read
A three-by-three grid of circles, squares and triangles in navy, gold and outline with the bottom-right cell missing, and six answer options labelled A to F: an original sample matrix question.Taking a Test

IQ Test Questions for Kids

Original IQ test questions for kids with answers, by age: sample items for 4-7, 8-12 and 13-17, a matrix puzzle worked through, how a child's score is set, how stable it is, and what practice really does.

12 min read
Three cards showing where 100 the average, about 40 a real test's practical floor, and 0 sit on the same deviation IQ scale, with zero about 6.7 standard deviations below the mean.Scores & Scales

Can Your IQ Be Zero?

Mathematically, the IQ scale has no floor built in - but no test has ever reported a zero. Where the deviation IQ scale actually stops working, why real tests bottom out around 40, and what a score that low would even require.

7 min read
Bar chart ranking average standardized test scores by college major across five US datasets from 1946 to 2014, with engineering, physical sciences and math or computer science highest and education lowest.Research & Evidence

Average IQ by College Major

Average test scores really do differ by college major, and the rank order has barely moved in 70 years. What a landmark cross-dataset analysis found, why SAT and GRE scores are not IQ scores, and what the ranking cannot tell you about one student.

6 min read
Bar chart comparing self-reported anxiety and mood disorder diagnosis rates between the general population, about 10 percent each, and a 2018 survey of 3,715 members of a high IQ society, about 20 percent anxiety and 27 percent mood disorder.Understanding IQ

High IQ and Mental Health

A widely cited 2018 study found sharply higher rates of anxiety and depression among members of a high-IQ society. Why that finding is far from the whole story, what a century of gifted research actually shows, and what seems to matter more than IQ itself.

6 min read
Four cards comparing testosterone and cognition findings across studies: no correlation in 8 year old boys, positive at age 10, negative at age 12, and no association with memory in older men in a Mendelian randomization study.Research & Evidence

IQ and Testosterone

A popular online chart claims a clean link between testosterone and IQ. Real studies disagree with each other on direction and size, and the most rigorous test found no effect at all. What the actual research says, and why the meme persists.

6 min read
Bar chart comparing estimated ADHD prevalence in general-population children, about 7.5 percent, and identified-gifted children, about 6.5 percent, showing the two rates are close.Understanding IQ

High IQ and ADHD

High IQ and ADHD can and do coexist, at close to the general-population rate. What twice-exceptional actually means, why the combination gets missed in both directions, and how ADHD can pull down a full-scale IQ score without touching real reasoning ability.

6 min read
Comparison of three highest-IQ figures: Marilyn vos Savant's 228 Guinness record, William James Sidis's unverified 250 to 300 estimate, and the roughly 155 to 160 ceiling of a modern IQ test.Scores & Scales

Highest IQ Ever Recorded

The highest IQ ever recorded is usually given as Marilyn vos Savant's 228 or William James Sidis's claimed 250 to 300 - neither from a test in use today. Where the famous numbers actually come from, and what a modern test can really report.

6 min read
Bar chart of validity coefficients for predicting job performance: years of education 0.10, years of experience 0.18, general cognitive ability 0.51 across jobs and 0.58 for high-complexity jobs, from Schmidt and Hunter 1998.Taking a Test

IQ Tests in Job Interviews

An IQ test for a job interview is usually branded a cognitive ability assessment, like the Wonderlic. What it actually measures, why a 1998 meta-analysis made employers take it seriously, whether it is legal, and how to prepare.

6 min read
Bar chart comparing average full-scale IQ of the general population, 100, with offender samples, 91, an approximately 9-point gap described in criminology research.Research & Evidence

IQ and Crime

IQ and crime show a real but modest correlation: offenders average eight to ten points lower than non-offenders. What actually drives the gap, including a specific environmental cause with its own evidence, and what the finding cannot tell you about any one person.

6 min read
Bar chart of breed-level heritability for four dog cognitive abilities: inhibitory control 0.70, communication 0.39, physical reasoning 0.21 and memory 0.17.Understanding IQ

Dog IQ

Dogs do not have an IQ: no validated test gives them one. Researchers can measure trainability, memory, self-control and a small general factor, and those results say more about how dogs think than any breed ranking, at-home dog IQ test or "as smart as a toddler" comparison ever could.

7 min read
Chart of the cognitive profile often seen in Down syndrome: relative strengths in visual and social skills, relative weaknesses in verbal memory, expressive language and executive function.Understanding IQ

Down Syndrome and IQ

Most people with Down syndrome score in the mild to moderate range of intellectual disability, with an average IQ of around 50 and a typical range of about 30 to 70. The number hides a wide spread, a consistent profile of strengths, and test limits that matter more here than almost anywhere else.

7 min read
Bar chart showing that an IQ of 140 is reached by 1 in 261 people on a standard deviation 15 scale, 1 in 161 on SD 16 and 1 in 21 on SD 24.Scores & Scales

What an IQ of 140 Means

An IQ of 140 sits 2.67 standard deviations above the mean, at about the 99.6th percentile: roughly one person in 261 scores that high. It clears the gifted line and most high-IQ society cutoffs, but no current test manual calls it genius, and a single 140 is far less exact than the number suggests.

7 min read
Bell curve with the lower tail shaded below IQ 70 and a highlighted band from 65 to 75 showing the measurement-error zone around the score.Scores & Scales

What an IQ of 70 Means

An IQ of 70 sits two standard deviations below the mean, at about the 2nd percentile. It is the score most often linked with intellectual disability, but a diagnosis never rests on the number alone: measurement error turns the line into a zone, and adaptive functioning decides who is inside it.

8 min read
Table converting SAT and ACT percentile rank into a predicted IQ score and IQ percentile.Scores & Scales

SAT and ACT Score to IQ Conversion

Neither the SAT nor the ACT is an IQ test, but studies found they correlate with general cognitive ability at 0.77 to 0.86. See predicted IQ by percentile for both tests, a worked example, IQ to SAT, and why any single conversion carries about 12 points of error either side.

11 min read
Chart showing cognitive outcomes improving in a gradient across gestational age categories from extremely preterm to full term.Research & Evidence

Premature Birth and IQ

Children born very preterm score, on average, about 0.8 of a standard deviation lower on IQ tests than children carried to term. Here is what a 2018 meta-analysis and the studies since actually found: the gestational-age gradient, what is really driving the gap, and what it does not tell you about one specific child.

6 min read
Diagram contrasting the single gene region behind eye color with the thousands of variants linked to measured intelligence.Research & Evidence

Eye Color and IQ

There is no credible study linking eye color to IQ, and the chromosome region that determines eye color has never turned up in a genome-wide study of intelligence. Here is what the genetics actually says, where the pattern people cite really comes from, and how it compares to a correlate that does have real evidence behind it.

6 min read
Table comparing cognitive and psychological domains where gifted children show a research-backed advantage against domains where they do not.Understanding IQ

Signs of a Gifted Child

The "reads early, has a big vocabulary" checklist misses what a 2024 systematic review actually found: an uneven cognitive profile, a documented speed-accuracy tradeoff, asynchronous development, and real gaps in who gets identified. What the research says, and what to do with a hunch.

6 min read
Bar chart of IQ point change per 1 microgram per cubic meter increase in PM2.5 air pollution: full-scale IQ down 0.27, performance IQ down 0.39, verbal IQ down 0.24, from a 2024 meta-analysis of 4,860 childrenResearch & Evidence

Air Pollution and IQ

A 2024 meta-analysis pooling six studies and 4,860 children found that every rise in fine-particle air pollution came with a small, statistically significant drop in IQ scores. The same pattern shows up in aging adults living near traffic, and in a household exposure route this conversation usually leaves out entirely.

6 min read
Bar chart comparing the reported IQ deficit from heavy prenatal smoking before and after adjusting for confounders: 4 points lower unadjusted, not statistically significant after adjusting for maternal IQ and other confounders, Danish National Birth Cohort 2012Research & Evidence

Prenatal Smoking and IQ

Several studies link smoking during pregnancy to a lower child IQ score. Then a Danish cohort of 1,782 mothers adjusted for the one variable most of the earlier research had not: the mother's own IQ. What was left afterward is a genuinely more complicated story than the headline number suggests.

6 min read
Bar chart comparing task-switching response times between heavy and light media multitaskers: heavy multitaskers 426 milliseconds slower on switch trials and 259 milliseconds slower on nonswitch trials, Stanford study 2009Research & Evidence

Multitasking and IQ

No study has measured a person's IQ before and after a bout of multitasking. What researchers at Stanford measured instead is narrower and more surprising: heavy multitaskers, tested against the exact skill they practice constantly, turned out to be worse at it, not better.

6 min read
Bar chart comparing verbal and total IQ scores in six-year-old boys by sleep duration: about 10 points higher in boys sleeping 10 or more hours a night versus boys sleeping less than 8 hoursResearch & Evidence

Sleep and IQ

This site's news desk has already covered what one bad night does to a test score on the day it is taken. This is a different and, for children especially, more consequential question: what years of too little sleep do to the cognitive systems an IQ test measures in the first place.

6 min read
Bar chart of executive-function deficits in fetal alcohol spectrum disorder versus typically developing peers, in standard deviation units: planning 0.94, fluency 0.87, set-shifting 0.87, working memory 0.84, vigilance 0.52, inhibition 0.50 below average, from Kingdon et al. 2016Research & Evidence

Fetal Alcohol Spectrum Disorder and IQ

A clinical study of 473 people diagnosed with fetal alcohol syndrome or its milder forms found that only 16 percent had an IQ in the intellectually disabled range. That statistic is not the reassurance it sounds like -- it is the reason the condition is so often missed. Here is what a normal-looking score can still be hiding.

6 min read
Bar chart of average IQ by care condition at age 4.5 in the Bucharest Early Intervention Project: 109 for never-institutionalized children, 81 for children randomly assigned to foster care, and 73 for children who remained in institutional careResearch & Evidence

Toxic Stress and IQ

Researchers in Romania did something that can never be done again for ethical reasons: they randomly assigned some institutionalized children to foster care and left others in the institution, then followed both groups for twenty years. The IQ gap that opened up has held at every check-in since. What has not held up as cleanly is the famous claim about exactly when the window closes.

6 min read
Bar chart comparing the reported bilingual executive-function advantage in children before and after correcting for publication bias: 0.08 standard deviations before correction, falling to negative 0.04, statistically indistinguishable from zero, after correction, from Lowe et al. 2021Research & Evidence

Bilingualism and IQ

For about a decade, a well-known finding held that bilingual children and adults show sharper executive function than monolinguals. Then researchers tried to replicate it across 15 separate measures and found almost nothing. A study of conference abstracts explained part of why the early evidence looked so much stronger than what came next.

6 min read
Timeline of IQ testing and eugenics: 1917 Army Alpha and Beta tests administered, 1923 Brigham publishes A Study of American Intelligence, 1924 Immigration Act restricts immigration by national origin, 1930 Brigham retracts his own conclusions, 1981 Gould publishes The Mismeasure of ManUnderstanding IQ

IQ Testing and Eugenics

Between 1917 and 1919, the United States Army tested roughly 1.75 million recruits in the largest intelligence-testing program the world had yet seen. Within a decade, one psychologist had turned that data into a case for restricting immigration by race. Thirteen years after that, the same psychologist published a retraction few people have ever heard of.

6 min read
Bar chart showing the breastfeeding-promotion group's IQ advantage shrinking from 7.5 points in verbal IQ and 5.9 points in full-scale IQ at age 6.5 to 1.4 and 1.2 points by age 16, from the PROBIT randomized trialResearch & Evidence

Breastfeeding and IQ

The largest randomized trial ever run on breastfeeding found a genuine IQ advantage at age six -- about six points on full-scale IQ. By age sixteen, the gap on most measures had shrunk close to zero. Here is what the trial actually measured, and why it still beats every observational study that came before it.

6 min read
Bar chart comparing Perry Preschool program and no-program groups at age 40: 65 versus 45 percent high school graduation, 64 versus 45 percent avoiding five or more arrests, and 49 versus 15 percent earning over 20,000 dollars, despite the early IQ advantage fading by age eightResearch & Evidence

Preschool and IQ

The most famous experiment in early-childhood education raised participants' IQ scores by as much as 13 points -- then watched that advantage shrink to almost nothing within a few years. Their income, education and arrest records stayed different for the rest of their lives. Why would outcomes outlast the score that supposedly predicts them?

6 min read
Two-panel bar chart comparing memory athletes and matched controls: 71 versus 40 words recalled after 20 minutes, but nearly identical fluid-reasoning scores of 128.1 versus 128.4Understanding IQ

Memory and IQ

The world's best memory athletes can memorize 71 shuffled words in twenty minutes. Their IQ scores are not measurably different from a matched control group who could only manage 40. If a spectacular memory is not the same thing as a high IQ, what actually is the difference?

6 min read
Bar chart comparing the rarity of Mensa, Triple Nine Society, Prometheus Society, and Mega Society admission thresholds, from 1 in 50 up to 1 in 1,000,000 of the populationScores & Scales

High-IQ Societies Explained

Mensa is the famous one, but it is nowhere near the most exclusive. The Triple Nine Society admits one person in a thousand; the Prometheus Society, one in thirty thousand. Here is how each threshold is actually set, what test you would need, and why the further out you go, the less any single number can be trusted.

6 min read
Bar chart comparing spousal correlation coefficients across trait categories, showing intelligence at 0.40, height and weight at 0.20, and personality traits at 0.10Research & Evidence

Assortative Mating and IQ

Married and long-term partners score more alike on IQ than on almost any other trait psychologists measure, personality included. The correlation is about 0.40, it shows up before the relationship starts, and it has real downstream effects on how heritability studies get interpreted.

6 min read
Timeline chart showing which IQ test applies at which childhood age, WPPSI from two and a half to seven, WISC from six to sixteen, and WAIS from sixteen onward, with the six to seven overlap band markedTaking a Test

IQ Testing for Children

Children are not tested on the same instrument as adults, and the test itself changes twice before age eighteen. Here is which one applies when, how reliable an early score really is, and what a parent should and should not conclude from a single number.

6 min read
Bar chart of correlations between chess skill and six cognitive abilities from a meta-analysis, ranging from 0.35 for numerical ability down to 0.13 for visuospatial abilityResearch & Evidence

Chess Ratings and IQ

Chess has a reputation as a proxy for raw intelligence. The best available meta-analysis puts the real correlation at a modest 0.24, and it gets noticeably weaker once you look only at ranked, adult tournament players.

6 min read
Bell curve chart of IQ scores with the population marked at 145, the three standard deviation boundary, and 160, the typical test ceiling, with the extrapolation zone beyond both shadedScores & Scales

IQ Score Ceiling Effects

Two different numbers get used as "the top of the scale," 145 and 160, and they come from two different kinds of limit. One is a statement about population statistics; the other is about what a specific test manual will actually compute.

6 min read
Chart of fluid and crystallized intelligence across the adult lifespan, showing fluid reasoning peaking in the mid-twenties and declining steadily while crystallized knowledge keeps rising into the sixtiesUnderstanding IQ

Fluid vs Crystallized Intelligence

Fluid intelligence is what you use on a problem you have never seen before. Crystallized intelligence is everything you have already banked. The distinction has survived eighty years of factor analysis because the two halves genuinely behave differently, and the clearest proof is what happens to each one as you get older.

6 min read
Chart showing how the heritability of IQ changes with family income in the Turkheimer 2003 twin study, with shared environment accounting for most variance in the poorest families and genes for most in affluent onesResearch & Evidence

Socioeconomic Status and IQ

Family circumstances track IQ scores, and the relationship is stranger than a simple gap. In the poorest families studied, genes explained almost none of the variation in childhood scores and shared environment explained most of it. In affluent families the pattern reversed. Here is what that finding does and does not support.

6 min read
Bar chart of the percentage of performance variance explained by deliberate practice in five domains, from 26 percent in games down to under 1 percent in professions, with the unexplained remainder shownResearch & Evidence

Talent vs Practice

The 10,000-hour rule made a strong claim: expert performance is built by practice, not given by talent. When researchers pooled the studies that had actually measured it, practice explained about a quarter of the difference between people in games and almost none in professional work. Here is what fills the rest of the gap.

6 min read
Chart comparing three waves of growth mindset evidence, showing a weak pooled intervention effect, a targeted national trial that worked for lower-achieving students, and a later review finding widespread biasResearch & Evidence

Growth Mindset and Intelligence

The claim that believing intelligence is malleable makes you achieve more is one of the most widely taught ideas in education, and one of the most heavily contested in the research literature. Three waves of evidence have now landed. Here is what each found, and the question none of them actually answered.

6 min read
Chart comparing machine and human performance across four task types, showing machines ahead on graduate science questions and coding, level on novel puzzle solving, and behind on tasks never seen beforeUnderstanding IQ

Is AI Smarter Than Humans?

Ask whether AI is smarter than humans and the honest answer depends entirely on the task. Frontier systems now beat expert humans on graduate-level science questions and lose to ordinary people on puzzles built to be unfamiliar. Here is what the 2026 benchmarks actually measure, and why one score never settles it.

6 min read
Chart of reported AI IQ figures from four different tests, ranging from below 100 on a culture-fair test to 155 on the verbal subtests of the Wechsler scale, showing how far the same systems spread across testsScores & Scales

What Is ChatGPT's IQ Score?

Search for ChatGPT's IQ score and you will find 155, 136, 116 and under 100, all reported seriously, sometimes for the same model. They are not contradictions to be resolved. They are different tests, scored different ways, and the spread between them is the most informative thing about the whole exercise.

6 min read
Chart of what the cognitive debt essay-writing study measured, showing lower brain engagement and weaker recall in the AI-assisted group, alongside the outcomes the study did not measure including IQMind & Everyday Life

Does Using AI Make You Dumber?

The claim that AI is making us stupider has real research behind it and is still routinely overstated. No study has measured a drop in intelligence. What has been measured is lower mental engagement during a delegated task and weaker memory for work you did not do yourself, which is a narrower finding and a more useful one.

6 min read
Chart comparing four published definitions of artificial general intelligence from OpenAI, Google, Microsoft and the ARC Prize Foundation, showing how little they overlap on what would countUnderstanding IQ

What Is AGI?

Artificial general intelligence means a system that can learn and apply knowledge across the full range of tasks a person can, rather than excelling at a narrow set. The trouble is that the major labs each publish a different definition, none of them converts into a test, and so claims that AGI has arrived cannot be checked either way.

6 min read
Bar chart comparing chess training study results, showing a moderate effect on general cognitive ability in studies with no active control group, shrinking to near zero in the better-designed studies that used oneMind & Everyday Life

Does Chess Raise Your IQ?

Chess is one of the oldest test cases for a big question: does practicing a demanding mental skill make you generally smarter, or just better at that skill? The honest summary from decades of research: real for chess itself, modest for a couple of related skills, and close to zero for general IQ.

6 min read
Horizontal bar chart of video game training effects by skill, showing a moderate improvement in spatial ability, a small improvement in executive function, and almost no measurable change in general intelligence test scoresMind & Everyday Life

Do Video Games Raise Your IQ?

Action video games produce real, replicated gains in spatial ability and attention, some of the best near-transfer evidence in this batch. Push the test further away, toward the general reasoning an IQ test measures, and the effect all but disappears once the research is pooled properly.

6 min read
Line chart of vocabulary size across school grades for three reading-volume groups, starting close together in early grades and fanning out into a wide gap by the later gradesMind & Everyday Life

Does Reading Raise Your IQ?

Reading volume and vocabulary growth are genuinely linked, and the relationship compounds over years rather than staying fixed. But it is mostly the verbal, crystallized side of ability that moves, not the abstract reasoning an IQ test also measures, and cause and effect run both ways.

6 min read
Bar chart of aerobic exercise effects on four executive function skills, showing real improvements in inhibitory control, working memory and cognitive flexibility, and no significant change in planningMind & Everyday Life

Does Exercise Raise Your IQ?

Aerobic exercise has some of the best-replicated cognitive evidence of any lifestyle factor, but not for a full IQ score. What reliably improves is executive function: working memory, inhibitory control, cognitive flexibility. One related skill, planning, barely moves at all.

6 min read
Bell curve of IQ scores with everything below 120 shaded, showing that about 91 percent of people score below that mark and about 9 percent score at or above itScores & Scales

Is a 120 IQ High?

A score of 120 sits comfortably above average, and roughly nine people in ten score below it. But "high" is a comparison, not a property, and the honest answer depends on which scale produced the number, how much error is wrapped around it, and what you were hoping the score would tell you.

6 min read
Two confidence intervals drawn on an IQ scale, one for a measured 97 and one for a measured 100, overlapping across almost their whole width to show that the two scores have not been told apartScores & Scales

Is 97 IQ Dumb?

A score of 97 is average. It sits three points below the population mean, which is well inside the margin of error of any test that produced it, so 97 and 100 are the same result in every way that can be measured. The interesting question is not what 97 says about you, but how little any single number can say.

6 min read
Bar chart of how rare each IQ score is, showing 1 in 2 at 100, 1 in 11 at 120, 1 in 44 at 130 and 1 in 261 at 140, with the bars shortening far faster than the scores riseScores & Scales

Is 130 IQ a Genius Score?

A score of 130 is the conventional threshold for gifted identification and for high-IQ society membership, and it is reached by about one person in 44. It is not, however, a "genius" score, because no published test defines such a band. The word is a popular import, and the difference is worth understanding.

7 min read
Bell curve of IQ scores with the region below 85 shaded and the separate threshold at 70 marked further to the left, showing about 16 percent at or below 85 against about 2 percent at or below 70Scores & Scales

What an IQ of 85 Means

A score of 85 sits exactly one standard deviation below the population mean, at roughly the 16th percentile. It is the bottom edge of what test manuals call low average, it is well clear of any clinical threshold, and on its own it says considerably less about a person than the number appears to.

6 min read
Chart showing the supralinear relationship between childhood blood lead concentration and IQ score, with the steepest loss occurring across the lowest range of exposure rather than the highestResearch & Evidence

Lead, Pollution and IQ

Most things people believe raise or lower intelligence turn out to be small, contested or confounded. Childhood lead exposure is the exception: one of the best-established environmental effects on cognitive test scores anywhere in the literature, with a dose-response curve most people find counterintuitive.

6 min read
Diagram contrasting the steep cognitive gain from correcting a nutritional deficiency with the flat response to supplementing an already adequate diet, shown as a curve that rises sharply and then plateausResearch & Evidence

Nutrition and IQ

The evidence on diet and intelligence looks contradictory until you separate two questions that get asked as one. Fixing a real deficiency produces some of the largest effects in the field. Adding more of the same nutrient to an already adequate diet produces close to nothing.

7 min read
Diagram distinguishing cultural bias in test items, which is a property of the questions, from stereotype threat, which is a property of the testing situation and the instructions given before itTaking a Test

Stereotype Threat and Test Scores

Few findings in psychology have been cited as widely, or held up as poorly, as stereotype threat. The original experiments were elegant and the idea is intuitive. Two decades of replication attempts have left a much smaller and more uncertain effect than the textbook version suggests.

6 min read
Diagram showing a confidence interval straddling the gifted cutoff of 130, illustrating how two children with different obtained scores can have overlapping true-score rangesScores & Scales

Gifted Cutoff Scores

Most gifted programmes draw their line at an IQ of 130. The number is a statistical convention rather than a boundary in nature, and three well-documented features of how the score is produced and used mean a strict cutoff reliably excludes children who belong on the other side of it.

6 min read
Diagram contrasting what an IQ test measures with what a rationality test measures, showing reasoning power on one side and belief calibration, myside bias and probabilistic thinking on the other, with only partial overlap between themMind & Everyday Life

Why Smart People Make Bad Decisions

Everyone knows someone brilliant who keeps making terrible calls. That is not a paradox; it is a measurement gap. Intelligence tests and rationality tests load on different things, and several of the best-studied thinking errors turn out to be almost completely independent of how high you score.

7 min read
Chart showing the three natural-experiment designs used to estimate the effect of schooling on IQ (policy change, school-age cutoff and control for earlier intelligence), each yielding an estimated gain of roughly one to five IQ points per additional year of educationResearch & Evidence

Does School Raise IQ?

Education is the environmental factor with the strongest evidence for actually raising IQ scores, and the effect is bigger than most people expect. Three independent study designs, pooled across more than 600,000 participants, point the same way. Here is the size of it, and the caveat that gets dropped.

6 min read
Diagram showing where processing speed sits in the structure of cognitive ability, with simple reaction time, choice reaction time and inspection time on one axis and their differing strength of association with general intelligence shown alongsideUnderstanding IQ

Processing Speed and IQ

Fast thinkers are assumed to be smart thinkers, and there is a real finding underneath the stereotype: people who score higher on IQ tests do respond faster on tasks with no reasoning content at all. But the link is weaker than the folklore, and on a professional battery the speed index is the least g-loaded.

6 min read
Annotated layout of a typical IQ test report showing the Full Scale IQ with its confidence interval, the index scores on a mean of 100, the subtest scaled scores on a mean of 10, and the percentile rank columnScores & Scales

How to Read an IQ Test Report

An IQ report puts numbers on at least three different scales and almost never explains which of them matters. Here is what FSIQ, the index scores, the subtest scaled scores, the percentile rank and that bracketed range each mean, and when the headline number should not be read at all.

7 min read
Diagram separating three things often confused under the word bias: a score gap between groups, item bias where equally able test-takers answer differently, and predictive bias where a score forecasts an outcome differently by groupResearch & Evidence

Cultural Bias in IQ Tests

Ask whether IQ tests are culturally biased and you get two confident, opposite answers. Both are partly right, because the word means something far narrower to a psychometrician than it does in ordinary use. Here is what the item-level evidence shows, and where culture really does get into a score.

7 min read
Chart contrasting six popular brain claims with what research found, showing the residual grain of truth in each: lateralisation without dominance, whole-brain activity, no meshing effect, no far transfer and a small brain size correlationUnderstanding IQ

Brain Myths About Intelligence

You are not left-brained or right-brained, you do not use ten per cent of your brain, and matching a lesson to your learning style does not help you learn. Six claims about intelligence that almost everyone repeats, what the studies that tested them found, and the smaller true fact hiding inside each one.

7 min read
Diagram of the positive manifold: a correlation grid showing that verbal, spatial, numerical and memory tests all correlate positively with one another, which is the finding multiple intelligences theory predicts should not appearResearch & Evidence

Gardner's Multiple Intelligences

Gardner's multiple intelligences theory is one of the most influential ideas in education and almost entirely absent from the tests psychologists use. That gap is not stubbornness. It comes down to one stubborn statistical finding, one missing instrument, and a real insight the theory carries.

7 min read
Chart showing that a correlation of 0.5 between IQ and school achievement accounts for about 25 per cent of the variation, with the remaining 75 per cent attributed to prior knowledge, conscientiousness, motivation, teaching quality and circumstanceResearch & Evidence

Does IQ Predict School Success?

IQ predicts school achievement better than any other single measure psychologists have found, and still leaves roughly three-quarters of the variation unexplained. Both halves of that sentence get ignored by somebody. Here are the actual correlations, what they mean for one child, and what accounts for the rest.

6 min read
Chart showing a verbal index of 118 and a non-verbal index of 103, each with its measurement error band, and the 15-point gap between them carrying a much wider band of roughly 4 to 26 pointsScores & Scales

Verbal vs Non-Verbal IQ Scores

Two people can hold the same IQ number and have completely different profiles, and a split between the verbal and non-verbal indexes is far commoner than most test-takers expect. Here is what base-rate tables and compounding measurement error say about how large a gap has to be before it means anything.

7 min read
Grid rating how far dyslexia, ADHD and autism affect four IQ test domains: verbal comprehension, processing speed, working memory and matrix reasoning, which is largely sparedTaking a Test

ADHD, Autism and Dyslexia in IQ Testing

A test score is a measurement, and a measurement can be biased by the conditions under which it is taken. ADHD, autism and dyslexia each depress performance on particular kinds of item without lowering the reasoning underneath. Here is what actually interferes, condition by condition, and what to do next.

7 min read
Bar chart comparing the twenty-point loss people claim test anxiety costs with the roughly three points the measured effect size impliesMind & Everyday Life

Test Anxiety and IQ Scores

Almost everyone who has had a disappointing result has wondered whether nerves cost them fifteen or twenty points. The evidence says no. Test anxiety and cognitive performance correlate at roughly r = -0.20, which works out to a few points on a 15-point scale. Here is the number, and what it changes.

7 min read
Chart of creative achievement against IQ, contrasting the threshold claim that the line goes flat above 120 with re-analyses showing it keeps rising more gentlyResearch & Evidence

IQ and Creativity

The threshold hypothesis says IQ and creativity move together up to about 120 and barely at all above it. It is a real claim with a real number, and modern re-analyses have weakened it. Here is what the segmented-regression work found, why the two kinds of task differ, and why measurement noise matters.

7 min read
Bell curve showing the top 2 percent of IQ scores that qualify for MensaScores & Scales

Mensa IQ Score Requirements

Mensa admits the top 2% of scorers, but "the top 2%" is a rank, not a number, and the number it maps to changes with the test you sat. Here is what qualifies on the Wechsler, Stanford-Binet and Cattell scales, the two routes to membership, and what the supervised admission test is actually like.

7 min read
Side by side comparison of what IQ measures and what EQ measuresMind & Everyday Life

IQ vs EQ

IQ measures reasoning; EQ measures how well you read and manage emotion. They are different constructs, measured in different ways, with different amounts of evidence behind them. Here is what each one actually predicts, which is easier to change, and where the popular claim that EQ matters more comes from.

6 min read
Comparison of the professional IQ tests psychologists use and what each measuresTaking a Test

Professional IQ Tests

When a psychologist measures intelligence, they reach for one of a small number of standardised instruments. This guide covers what the Wechsler scales, Stanford-Binet, Woodcock-Johnson and Raven's Progressive Matrices each measure, who each one is for, and where an online test genuinely fits.

6 min read
Chart showing how the heritability of IQ rises from childhood to adulthoodResearch & Evidence

Is IQ Genetic?

Heritability estimates for IQ rise from roughly 0.4 in childhood to 0.7 or higher in adulthood, which sounds decisive until you know what heritability measures. Here is what twin and adoption studies actually show, and the four conclusions people draw from them that the statistic does not support.

7 min read
What Is Genius IQ LevelScores & Scales

What Is Genius IQ Level

It is highly recommended that you seek out the assistance of a psychologist or educational specialist who can boost your IQ to the level of a genius

7 min read
Ranges of IQ LevelScores & Scales

Ranges of IQ Level

IQ ranges are bands of scores on a scale where 100 is average and one standard deviation is 15 points. See every range from below 70 to 145 and above, the percentile each score reaches, how rare it is and why the same number changes between tests.

7 min read
IQ Scale for AdultsScores & Scales

IQ Scale for Adults

In intelligence, we eagerly await the day when human mind secrets are exposed. This article will discuss the Adult IQ Scale, a powerful tool for assessing intelligence and revealing latent skills.

7 min read
IQ Score Ranges Explained: What Your IQ Number Really MeansScores & Scales

IQ Score Ranges Explained: What Your IQ Number Really Means

The range of an IQ test is the span of scores it can report: about 40 to 160 for the major individually given tests. See the range by test, the percentile and band for every score from 85 to 145, why online tests report numbers outside the range and how far a score can move between sittings.

10 min read
IQ Level ChartScores & Scales

IQ Level Chart

An IQ level chart maps each score to its percentile, rarity and level. This one runs from 40 to 160 in steps of 5, shows how many people in 1,000 fall in each level, explains how to read it for children and adults, and notes what a chart cannot tell you.

7 min read
IQ ClassificationsScores & Scales

IQ Classifications

IQ classification sorts scores into named bands, and the names depend on the test: Average is 90 to 109 on the Wechsler scales, but 130 and above is Very Superior on one test and Extremely High on another. See the labels side by side, where they came from and what they do not mean.

11 min read
IQ Tests and Gender Differences: Fact or Fiction?Research & Evidence

IQ Tests and Gender Differences: Fact or Fiction?

The idea that men perform better on IQ tests that evaluate cognitive abilities has helped spread this idea.

4 min read
The Importance of IQ Tests in Education and EmploymentResearch & Evidence

The Importance of IQ Tests in Education and Employment

Academic achievement and professional success are of the utmost importance in today’s competitive employment market. Important to this strategy is the IQ test

6 min read
How to Prepare for an IQ Test?Taking a Test

How to Prepare for an IQ Test?

You cannot revise for an IQ test like a school exam, but preparation helps: know the question types, practise on similar items, pace yourself and sleep. Retesting raises scores by about 4 points on average. See what to practise and what to skip.

9 min read
What Your IQ Test Score Really Means?Scores & Scales

What Your IQ Test Score Really Means?

An IQ score is your position among other people on a scale where 100 is the average, not a measure of how much intelligence you hold. See what each range means, how much error a score carries, why tests disagree and what a score can and cannot predict.

9 min read
Is Intelligence limited to IQ?Understanding IQ

Is Intelligence limited to IQ?

As we explore the fascinating world of intelligence, we will uncover the truth about IQ and the limitations of the human intellect. Beyond traditional measures of intellect, this article explores a wider range of aptitudes that impact our perception and engagement with the natural world.

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Which Part of the Brain, IQ Tests MeasuresUnderstanding IQ

Which Part of the Brain, IQ Tests Measures

Finally, IQ tests focus on certain regions of the brain to reveal the chemical basis of intelligence. If we want to know how we gain intelligence, we must study the roles and connections between these domains. It is essential to recognize that IQ tests have limitations, and a more thorough assessment of intelligence is necessary.

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What Are The Type of Questions Asked On IQ Test?Taking a Test

What Are The Type of Questions Asked On IQ Test?

IQ tests ask a small set of question types: pattern and matrix reasoning, verbal reasoning, number series, spatial puzzles, working memory and speed tasks. See what each looks like, how many questions a test has and which tests are multiple choice.

7 min read
What are the Factors that Affect the Results of an IQ Test?Research & Evidence

What are the Factors that Affect the Results of an IQ Test?

Anxiety, practice, old norms, schooling, lead exposure, sleep and genes all move an IQ result, by very different amounts. See the size of each effect, which factors act on the day of the test, which build up over childhood and whether your IQ changes over time.

7 min read
How to Know Our Mental Ability ?Understanding IQ

How to Know Our Mental Ability ?

This course is perfect for you if you want to learn how to concentrate better, remember more, or sharpen your brainpower. Discover the science behind developing your cognitive abilities and get practical advice and exercises to help you reach your full mental potential.

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What is a Genius IQ Score On An IQ Scale ?Scores & Scales

What is a Genius IQ Score On An IQ Scale ?

There is no official genius IQ score. The label comes from Terman in 1916 and is usually put at 140, about 1 person in 261. See how rare each score from 130 to 160 is, where the line sits on current tests, why no test measures far above 155 and what famous scores really are.

7 min read
How long is IQ test valid?Taking a Test

How long is IQ test valid?

Do you want to know how long an IQ test is valid for? Have you ever wondered how accurate it is and how it affects your IQ? Stop searching now. To better understand the significance of IQ test results, this article will investigate the validity period of these assessments.

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What Makes IQ Test Reliable ?Taking a Test

What Makes IQ Test Reliable ?

A reputable IQ test has three things: standardisation, reliability and validity. See what each means, the reliability figures the publishers report for the WAIS-IV, WISC-V, Stanford-Binet 5, WJ V and WPPSI-IV, what makes a test less reliable and how to judge any test you are offered.

8 min read
What Age is Most Accurate to Take an IQ Test?Taking a Test

What Age is Most Accurate to Take an IQ Test?

Scientists, teachers, and parents have always wondered how intelligence works. Although intelligence tests are widely accepted as credible measures of mental capacity, the scientific community disagrees on the best age to take one.

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Do IQ test really work?Taking a Test

Do IQ test really work?

IQ tests work for what they were built to do: rank reasoning ability against a norm sample and predict school results. See how accurate one score is, what the evidence says about validity, where tests fail, whether online IQ tests count and how to read a result.

8 min read
Pros and Cons of IQ TestingResearch & Evidence

Pros and Cons of IQ Testing

We hope that examining IQ testing from both pro and con perspectives will help you appreciate its challenges and how they effect people and communities. Why not join me on this intellectual adventure?

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What is Average IQ Test Score?Scores & Scales

What is Average IQ Test Score?

The average IQ test score is 100 by definition. About half of people score 90 to 109 and about 68% score 85 to 115. See the average range on each chart, why the average stays at 100, how scales differ and where to find averages for groups.

9 min read
History of IQ Testing: Origins to SignificanceResearch & Evidence

History of IQ Testing: Origins to Significance

Discover the strange history of IQ testing to assess its significance. Intelligence testing has impacted our knowledge of cognition and human potential since its inception. Expect a fascinating history of this statistic and its social effects.

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What Are The Advantages of IQ Test?Research & Evidence

What Are The Advantages of IQ Test?

The main advantages of IQ testing are a standard way to compare reasoning ability, early identification of learning needs and giftedness, group-level prediction of school and work results, and a profile of strengths and gaps. See each benefit, the evidence behind it and where it stops.

7 min read
What is Intelligence Quotient \(IQ\)?Understanding IQ

What is Intelligence Quotient (IQ)?

Intelligence quotient (IQ) is a score that compares a person's reasoning with others of the same age, set so the average is 100. See what IQ stands for, the ratio and deviation formulas with worked examples, who invented it, what tests measure and how to read a score.

8 min read
Unravelling Your Mind: Your Guide to Good Online IQ TestsTaking a Test

Unravelling Your Mind: Your Guide to Good Online IQ Tests

While the validity of online IQ tests can be debated, the desire to challenge ourselves and understand our cognitive abilities remains universal.

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Are IQ Tests Reliable Measures of Intelligence?Taking a Test

Are IQ Tests Reliable Measures of Intelligence?

It is crucial to understand that while IQ tests are not exhaustive measures of intelligence, they are reliable tools for assessing certain cognitive abilities.

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Cognitive Diversity: The Secret to Workplace Efficiency and SuccessMind & Everyday Life

Cognitive Diversity: The Secret to Workplace Efficiency and Success

Are you ready to explore the cognitive diversity within your organization? Discover how IQMetrics can help you unlock the potential of your workforce.

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How to Use Your IQ Test for Better Self-ImprovementMind & Everyday Life

How to Use Your IQ Test for Better Self-Improvement

Remember, an IQ test score is a starting point, not a limitation. Embrace it as a tool for understanding and nurturing your unique talents and potential.

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Cracking the IQ Code: Strategic Steps for Acing Your IQ TestsTaking a Test

Cracking the IQ Code: Strategic Steps for Acing Your IQ Tests

Preparation for an IQ test involves a journey of self improvement that’s more than just the exam itself. It’s a process of harnessing your cognitive skills and applying them to real life situations.

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Mind Matters: The Surprising Link Between Emotions and IQ Test ScoresScores & Scales

Mind Matters: The Surprising Link Between Emotions and IQ Test Scores

In your journey towards intellectual excellence, remember: understanding and managing your emotions is as important as sharpening your cognitive abilities. Embrace this holistic approach, and you are bound to not only excel in IQ tests but also thrive in life’s myriad challenges.

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Brainpower Unleashed: Unconventional Ways to Increase Your IQUnderstanding IQ

Brainpower Unleashed: Unconventional Ways to Increase Your IQ

How can I increase my IQ?” is a question which is asked very often and several professionals recommend conventional methods like puzzles, mental exercises, and a nutritious diet, but what if I tell you that we have some out of the box methods that can help us increase our IQ.

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Discovering High IQ: Key Signs, Expert Insights, and Practical AnalysisUnderstanding IQ

Discovering High IQ: Key Signs, Expert Insights, and Practical Analysis

In a world filled with diverse minds, the concept of intelligence has always been a source of fascination. Let’s embark on a captivating journey into the intriguing realm of high IQ.

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Decoding Intelligence: The 5 Ground-breaking Theories Shaping Modern IQ TestingUnderstanding IQ

Decoding Intelligence: The 5 Ground-breaking Theories Shaping Modern IQ Testing

Here at IQ Metrics, we understand the game-changing potential of these kinds of discoveries. Based on these notions, our examinations serve as more than just evaluations

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The Evolution of IQ Testing: Past, Present, and Future InsightsResearch & Evidence

The Evolution of IQ Testing: Past, Present, and Future Insights

Assessment of intelligence quotient (IQ) has been a topic of considerable discourse within the captivating domain of cognitive science.

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Hollywood Celebrities and their Hidden TalentMind & Everyday Life

Hollywood Celebrities and their Hidden Talent

Hollywood Celebrities and their Hidden Talent Welcome, readers! Today, we delve into the intriguing world of celebrities and explore the importance of IQ tests in their lives. Join us as we uncover the hidden talents and intellectual prowess of renowned personalities who have taken the plunge and revealed their IQ scores. Let’s discover how these…

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The Importance of Taking IQ Tests: Unlocking the Power of AssessmentResearch & Evidence

The Importance of Taking IQ Tests: Unlocking the Power of Assessment

The Importance of Taking IQ Tests: Unlocking the Power of Assessment Hello there, intellectuals! Today, we discuss into the significance of taking IQ tests and explore why these assessments play a crucial role in personal development, education, and society as a whole. Join us as we uncover the reasons behind the importance of IQ tests…

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Exploring the Fascinating World of IQ TestsUnderstanding IQ

Exploring the Fascinating World of IQ Tests

Exploring the Fascinating World of IQ Tests Welcome, readers! Today, we’re delving into the intriguing realm of IQ tests. Join us as we embark on a journey to understand what IQ tests are, how they work, and why they continue to captivate both researchers and individuals seeking to gauge their intellectual powers. What is an…

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New here

Three articles that make the rest make sense

Read these in order and the numbers on every other page stop being guesswork.

01What is Intelligence Quotient (IQ)?What IQ actually measures, and what it does not.02IQ Score Ranges Explained: What Your IQ Number Really MeansWhat a specific number means on a specific scale.03How to Prepare for an IQ Test?What helps before a test — and what does not.
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