The Flynn Effect Explained
The Flynn Effect is the systematic rise in average IQ scores recorded across the 20th century — about three points per decade in most industrialized countries. It is named for the political scientist James Flynn, who collated raw score data from dozens of national norming samples and showed that test-makers had been quietly adjusting raw-to-IQ conversions upward to keep the mean at 100.
The Flynn Effect is the systematic rise in average IQ scores recorded across the 20th century — about three points per decade in most industrialized countries. It is named for the political scientist James Flynn, who collated raw score data from dozens of national norming samples and showed that test-makers had been quietly adjusting raw-to-IQ conversions upward to keep the mean at 100. Without the recalibration, the average person in 2000 would have scored about IQ 120 on the 1932 Stanford-Binet.
The effect is largest on fluid-reasoning measures (matrix reasoning, similarities, abstract pattern items) and smallest or absent on crystallized-knowledge measures (vocabulary, general information, arithmetic facts). This pattern suggests that the rise reflects changes in the cognitive environment of modern life — more abstract reasoning demands, more schooling, better nutrition, less infectious disease in childhood — rather than a uniform increase in cognitive ability.
Several explanations have been proposed and partially supported. Improvements in prenatal and early-childhood nutrition account for some of the gain. Universal schooling, with its emphasis on abstract symbol manipulation, accounts for more. The cognitive demands of modern work — managing computers, navigating bureaucracies, parsing complex media — provide ongoing exercise for the abilities that fluid-reasoning tests measure. Reductions in childhood infectious disease and lead exposure also play a role.
Notably, the Flynn effect appears to have stalled or even reversed in some Northern European countries since the 1990s. Norwegian and Danish military induction data show declining mean IQ scores in cohorts born after 1975, with the decline concentrated in the same fluid measures that rose most steeply earlier in the century. The causes of the reversal are debated — possibilities include changes in education style, screen-media exposure, family-size and birth-order effects, or measurement artifacts.
For users of online IQ tests, the Flynn effect has a practical implication. Norms age. A test that was calibrated against 1990 data will overestimate scores by roughly three points per decade for a contemporary test-taker. This is one reason responsible test publishers re-norm their batteries every 10 to 15 years, and one reason an old IQ score from 30 years ago should not be directly compared to a new one without correction.