Flynn effect
Also known as: the flynn effect
The Flynn effect is the observation that average scores on intelligence tests rose steadily from one generation to the next throughout much of the twentieth century. Named for researcher James Flynn, the gains ran roughly three IQ points per decade across many countries.
James Flynn documented the pattern in the 1980s by examining the raw score data that test publishers collect each time they restandardize an intelligence test. Because IQ tests are normed so that the average of the current standardization sample equals 100, rising raw performance is invisible until you compare cohorts against a single fixed standard. When Flynn did that, he found that people were answering more items correctly, decade after decade, in every industrialized nation with usable records.
The gains were uneven across abilities. Increases were largest on tests of abstract, fluid reasoning — matrix problems such as Raven's Progressive Matrices that require finding patterns in unfamiliar material — and much smaller on crystallized measures such as vocabulary and arithmetic knowledge. That pattern makes a change in the underlying gene pool implausible over so few generations. Proposed explanations center on environment: better nutrition and health care, more years of formal schooling, smaller family sizes, greater exposure to abstract and symbolic thinking in work and media, and general familiarity with test-taking itself.
The practical consequence is that intelligence tests must be renormed periodically. Scoring someone against decades-old norms inflates their IQ, which matters in high-stakes settings such as eligibility determinations for services. Flynn himself cautioned that rising scores do not straightforwardly mean people are becoming more intelligent in every sense — the effect may reflect a growing habit of thinking in the abstract categories that IQ tests reward. Research since the 1990s has found the gains slowing, stopping, or reversing in several developed countries, a pattern sometimes called a negative Flynn effect.
AP Psychology tests the Flynn effect in its cognition and intelligence unit. Be ready to state what the effect refers to, identify environmental rather than genetic explanations, and connect it to why standardized tests require periodic restandardization.
Key takeaways
- The Flynn effect refers to the generational rise in average intelligence test scores, roughly three IQ points per decade.
- Gains were largest on abstract, fluid reasoning tasks and smallest on vocabulary and arithmetic.
- Environmental explanations — nutrition, education, smaller families, and more abstract thinking — are favored over genetic ones.
- The effect requires intelligence tests to be renormed regularly, and it has slowed or reversed in some countries.