Research & methodology

Learn about IQ testing

Reference material on intelligence testing, scoring methodology, and the research behind each cognitive domain.

What Is IQ?

The history and meaning of the intelligence quotient, from Binet to modern psychometric testing.

What each IQ range means, with percentiles, classifications, and rarity statistics.

Two components of cognitive ability, how they change with age, and which domains measure which.

The gold-standard culture-fair intelligence test, created in 1936 and still used worldwide.

The math behind the number: normal distributions, z-scores, percentiles, and the Flynn effect.

Enter any IQ score to see the percentile rank, classification, and position on the bell curve.

Mensa entry criteria, accepted tests, the application process, and what the proctored test is like.

How IQ varies by age and population, the Flynn effect, and why cross-country comparisons mislead.

Twin studies, heritability estimates, environmental factors, and why nature-versus-nurture is the wrong framing.

What separates a reliable test from a novelty one, and how to evaluate whether a given score means anything.