Category Archives: IQ

Genetic Scores and Average IQ

Source: Infoproc website, Oct 2016

This graph was in the comments

Database of IQ Studies

Source: Psychological Comments, Oct 2016

The database gives the Country, the age of the testees, the N, the test, the IQ, the short and the full reference, and then a column indicating whether we have an copy  of the reference (Y or N). Occasionally there are question marks where a reference has not been traced.

Database LINK

Rationality and Intelligence

Source: NYTimes, Sep 2016

irrationality — or what Professor Stanovich called “dysrationalia” — correlates relatively weakly with I.Q.

A person with a high I.Q. is about as likely to suffer from dysrationalia as a person with a low I.Q. In a 2008 study, Professor Stanovich and colleagues gave subjects the Linda problem and found that those with a high I.Q. were, if anything, more prone to the conjunction fallacy.

Sex Differences in IQ – Richard Lynn

Source: Psychological Comments, Sep 2016

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Sex Differences in Math and Science abilities

Source: Sage, Aug 2007

Sex differences in science and math achievement and ability are smaller for the mid-range of the abilities distribution than they are for those with the highest levels of achievement and ability. Males are more variable on most measures of quantitative and visuospatial ability, which necessarily results in more males at both high- and low-ability extremes …

Males outperform females on most measures of visuospatial abilities, which have been implicated as contributing to sex differences on standardized exams in mathematics and science.

We conclude that early experience, biological factors, educational policy, and cultural context affect the number of women and men who pursue advanced study in science and math and that these effects add and interact in complex ways.

Confidence, Persistence and Early Parental Encouragement

Source: Stanford alumni mag, Jul/Aug 2000

Though the Terman kids were handpicked for high IQ, the longitudinal results tell us little about the meaning of IQ, except for one study conducted by Terman’s associate, Melita Oden.

In 1968, she compared the 100 most successful and 100 least successful men in the group, defining success as holding jobs that required their intellectual gifts. The successes, predictably, included professors, scientists, doctors and lawyers. The non-successes included electronics technicians, police, carpenters and pool cleaners, plus a smattering of failed lawyers, doctors and academics.

But here’s the catch: the successes and non-successes barely differed in average IQ. The big differences turned out to be in confidence, persistence and early parental encouragement.

Genetics and IQ: 5 Findings

Source:, Sep 2014

five genetic findings that are special to intelligence differences and that have important implications for its genetic architecture and for gene-hunting expeditions.

  1. The heritability of intelligence increases from about 20% in infancy to perhaps 80% in later adulthood.
  2. Intelligence captures genetic effects on diverse cognitive and learning abilities, which correlate phenotypically about 0.30 on average but correlate genetically about 0.60 or higher.
  3. Assortative mating is greater for intelligence (spouse correlations ~0.40) than for other behavioural traits such as personality and psychopathology (~0.10) or physical traits such as height and weight (~0.20). Assortative mating pumps additive genetic variance into the population every generation, contributing to the high narrow heritability (additive genetic variance) of intelligence.
  4. Unlike psychiatric disorders, intelligence is normally distributed with a positive end of exceptional performance that is a model for ‘positive genetics’.
  5. Intelligence is associated with education and social class and broadens the causal perspectives on how these three inter-correlated variables contribute to social mobility, and health, illness and mortality differences.

These five findings arose primarily from twin studies. They are being confirmed by the first new quantitative genetic technique in a century—Genome-wide Complex Trait Analysis (GCTA)—which estimates genetic influence using genome-wide genotypes in large samples of unrelated individuals. Comparing GCTA results to the results of twin studies reveals important insights into the genetic architecture of intelligence that are relevant to attempts to narrow the ‘missing heritability’ gap.

Intelligence … is also one of the most stable behavioural traits, yielding a correlation of 0.63 in a study of people tested at age 11 and then again at age 79.

for intelligence, heritability increases linearly, from (approximately) 20% in infancy to 40% in adolescence, and to 60% in adulthood. Some evidence suggests that heritability might increase to as much as 80% in later adulthood47 but then decline to about 60% after age 80.48

A meta-analysis of 11000 pairs of twins shows that the heritability of intelligence increases significantly from childhood (age 9) to adolescence (age 12) and to young adulthood (age 17).