Psychology › Personality & intelligence › Intelligence and the g factor
The Flynn effect: rising IQ scores
1984; stalling since the 1990s· Finding or experiment
Well replicatedStrong, repeated evidence.
Raw scores on IQ tests rose about three points per decade through much of the 20th century in many countries.
See it on the Psychology map →What it says
In 1984 James Flynn, a US-born political scientist in New Zealand, showed Americans scored higher each decade against old test norms; in 1987 he documented gains in 14 nations. The rise was biggest on abstract reasoning puzzles, smaller on vocabulary and arithmetic. Likely causes include better nutrition and health, more schooling, smaller families and a world demanding abstract thought. Since the 1990s gains have stalled or reversed in Norway, Denmark, Finland and elsewhere. The name came from The Bell Curve (1994).
Why it matters
A gain of about 15 points in two generations is far too fast for genes, showing that intelligence test scores respond strongly to environment.
The evidence
Military conscript data from Norway, Denmark and the Netherlands, plus test standardization samples; a 2015 meta-analysis covering about four million people. A 2018 Norwegian study found the reversal within families, pointing to environment.
Open questions
Whether the gains reflect higher general intelligence or narrower test skills, and what drives recent declines, whether screens, schooling, test motivation or something else, is unsettled.
Connections (2)
▸The Flynn effect: rising IQ scores forced renorming of IQ testsWell replicated
The connection
Because average raw performance rose about three points a decade, tests scored against old norms gave inflated IQs, so publishers re-standardize every 10 to 20 years. It matters in court: an outdated norm can push a defendant's score above the cutoff for intellectual disability.
Who showed it and when
Flynn compared Stanford–Binet and Wechsler standardization samples in 1984; US courts have debated adjustments since the Supreme Court's 2002 Atkins v. Virginia ruling.
The evidence
People who take an old and a new version of the same test reliably score higher on the old one, matching Flynn's estimates.
Open questions
Whether courts should adjust individual scores for norm age is legally contested, and recent reversals complicate future norming.
▸The Flynn effect: rising IQ scores complicates simple readings of Heritability: nature and nurtureWell replicated
The connection
IQ is substantially heritable within a generation, yet average scores rose about 15 points in a few generations, far too fast for genetic change. This shows heritability says nothing about what causes average differences across time or between groups; environments can still shift a whole population.
Who showed it and when
Flynn and economist William Dickens proposed a resolution in 2001: small advantages draw people into richer environments, multiplying their effects.
The evidence
Gains appeared within decades in many countries' conscript records, too fast for genes; recent within-family declines also point to environment.
Open questions
What exactly caused the gains is still debated, as is what the effect implies for contested arguments about group differences in average scores.