IIF Certified Assessment
Start IQ Test
IIF Certified Assessment
New peer-reviewed findings on how reasoning, memory and general ability actually work — reported with the sample size and the error bars.
A full-scale IQ is not one thing a test measures directly. It is a composite built from several index scores, and the theory that decides which ones is called Cattell-Horn-Carroll — CHC for short.
Cognitive tests correlate less strongly with each other among high scorers than among low scorers. If that holds, a single full-scale figure carries less information the higher it goes — and the evidence for it is real but smaller and shakier than the idea's popularity suggests.
Savant syndrome pairs an ordinary or low Full-Scale IQ with one narrow ability that is exceptional, and it is the clearest case for why the index profile matters more than the total.
The largest synthesis of the question pooled 88 imaging studies and put the association between brain volume and IQ at roughly 0.24. That is about six per cent of the variation in scores, which is enough to rule out the strong claim and the flat denial at the same time.
Scores on tests that look nothing alike still correlate positively with one another. g is the factor pulled out of that pattern — which is what makes a single summary number defensible, and also what makes it far less than the whole story.
Average scores climbed for decades, then flattened and in places slipped. None of it shows on a score report, because every test is reset so the average is 100 again — which is why a 1990 score is not a 2026 score.
The correlation between them is one of the sturdier findings in cognitive psychology. How strong it is, and what it implies about training either one, is where the agreement stops.
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.
Each story ends with the studies, datasets and documents it draws on, named and attributed, so you can go and read them yourself.
Spotted an error? Write to corrections@iqmetrics.org. Corrections are made on the story and noted at the bottom of it — never quietly.
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 →
