Intelligence research,
reported plainly
Cognitive science, testing standards and the numbers behind them — written for a general reader, with every score carrying the scale it was measured on and the range around it.
Top story
Puzzles & Brain Training →
Puzzles & Brain TrainingCognitive Reflection Test: What the Bat-and-Ball Score Says About IQ
Across 3,428 people the three-question Cognitive Reflection Test averaged 1.24 correct, and only 17% got all three. Its link to IQ is moderate, not one-to-one, and the questions are now so well known that familiarity shifts scores.
Latest stories
All news →
Does Iodine Deficiency Lower IQ? What Trials and Cohorts Show
Severe deficiency costs roughly 7 to 12 IQ points in group studies. For the mild deficiency found in richer countries, a UK cohort links it to weaker verbal scores, the main pregnancy trial found no effect, and a Cochrane review in September 2026 found a slight gain in children.
ISEE Scores Explained: Scaled Scores, Stanines and the IQ Question
The ISEE reports four section scores of 760 to 940, a percentile and a stanine for each, and no total or pass mark. Its maker never calls it an IQ test, and its percentiles compare a child with other private-school applicants.
Has AI Passed the Turing Test? What the 2026 PNAS Study Found
A peer-reviewed PNAS paper says GPT-4.5, given a humanlike persona, was picked as the human in 73% of five-minute chats. Without the persona it managed 36%, and the authors say the test measures humanlikeness, not intelligence.
Does Creatine Raise IQ? What the Trials Show About Memory and Reasoning
One 2003 trial in 45 vegetarians started the claim. A preregistered replication in 123 people did not confirm it on the same test, and the EU food safety panel says no cognitive effect is established.
What Is a Good Predictive Index Cognitive Assessment Score?
PI scores run from 100 to 450, and its own blog says the average of 250 is about 20 of 50 questions right. PI says it is not a test you pass or fail, no longer shows percentiles, and does not measure IQ.
Average Reaction Time by Age, and What It Says About IQ
A typical simple reaction time is roughly 200 to 270 milliseconds, but the device and the task move it more than age does. In UK samples it correlates about -.3 with a timed intelligence test.
How Many Words Does the Average Person Know? Vocabulary Size and IQ
The best-documented answer is about 42,000 lemmas for an average 20-year-old native English speaker, from only 11,100 word families. The number changes with what you count, and vocabulary is among the most g-loaded parts of an IQ test.
Which MBTI Type Has the Highest IQ? What the Studies Show
The INTJ 130 and INTP 129 charts name no sample and no test. The best evidence finds a small IQ edge for Intuitive types, tied to openness, and the MBTI's publisher says it does not measure ability.
What Is a Good SHL Test Score? Percentiles, Norm Groups and IQ
SHL says it sets no passing score and its support team cannot give you your result. What its own reports show is a percentile against a named comparison group, with T and Sten scores derived from it.
Nine beats, one standard of evidence
Each desk covers a subject we can report on continuously and check against a source. Pick the one you care about — or read everything.
Intelligence Research
New peer-reviewed findings on how reasoning, memory and general ability actually work — reported with the sample size and the error bars.
Brain Health & Aging
Sleep, exercise, diet, illness, medication and environment — what each one measurably does to thinking, and by how much.
AI & Machine Intelligence
How machine reasoning is measured, where it beats people, where it still fails, and what any of it says about human intelligence.
Education & Testing
Admissions exams, gifted programs, national score reports and school testing policy, explained without the spin from either side.
Work & Hiring Tests
The cognitive and aptitude tests employers use, how they are scored, and what a score does and does not predict at work.
Data & Rankings
Chart-led pieces on how scores are distributed across countries, states, ages, jobs and education levels — always with the caveats attached.
Scores & Scales Explained
What a specific number means on a specific scale, why every score needs a confidence range, and how the scales convert.
Myths & Fact Checks
Viral IQ claims checked against the record: where the number came from, who repeated it, and what is actually documented.
Puzzles & Brain Training
A reasoning puzzle every day with the full working shown, plus honest coverage of what brain-training products can and cannot do.
Intelligence Research
All Intelligence Research →Average Reaction Time by Age, and What It Says About IQ
A typical simple reaction time is roughly 200 to 270 milliseconds, but the device and the task move it more than age does. In UK samples it correlates about -.3 with a timed intelligence test.
Does IQ Above 120 Stop Mattering? What a 50-Year Study Found
The "threshold hypothesis" holds that intelligence stops predicting achievement past roughly 120. A 50-year study tracking thousands of gifted 13-year-olds into midlife found the opposite: finer differences within the top 1% still predict who earns a doctorate, a patent or tenure.
Childhood Adversity and Cognition: What a PNAS Study Found
A September 2026 PNAS study scanned people aged 0 to 21 and linked stressful life events to one brain circuit and cognition to another. The effects are small, and one did not replicate.
Brain Health & Aging
All Brain Health & Aging →Does Iodine Deficiency Lower IQ? What Trials and Cohorts Show
Severe deficiency costs roughly 7 to 12 IQ points in group studies. For the mild deficiency found in richer countries, a UK cohort links it to weaker verbal scores, the main pregnancy trial found no effect, and a Cochrane review in September 2026 found a slight gain in children.
Does Creatine Raise IQ? What the Trials Show About Memory and Reasoning
One 2003 trial in 45 vegetarians started the claim. A preregistered replication in 123 people did not confirm it on the same test, and the EU food safety panel says no cognitive effect is established.
Does Weed Lower IQ? What the Long-Term Studies Actually Show
The best-known study found a drop of about 6 IQ points in people with repeated cannabis dependence. Twin studies, adjusted analyses and a 2026 teen study paint a more mixed picture. Here are the numbers, and what nobody has shown yet.
Written to be checked, not just clicked
Every number carries its scale
An IQ figure is meaningless without the scale it was measured on and the range around it. Every story here reports all three, or says plainly that the source did not.
Sources are listed, not implied
Each story ends with the studies, datasets and documents it draws on, named and attributed, so you can go and read them yourself.
We correct in public
Spotted an error? Write to corrections@iqmetrics.org. Corrections are made on the story and noted at the bottom of it — never quietly.
Read the research.
Then find your own number.
Our IIF-certified assessment reports your score with its scale, percentile and confidence range — and a breakdown of the cognitive domains behind it.
Start IQ Test →