The Flynn effect
For most of the 20th century, average scores on IQ tests rose by about 3 points every decade.
What was found
IQ tests are re-scaled every so often so the average stays at 100. When researchers compared new groups of people with the old scales, they kept finding the same thing: each generation scored higher than the last. The political scientist James Flynn documented these gains across 14 countries in 1987, and the pattern became known as the Flynn effect.
The gains were biggest on abstract reasoning puzzles, like pattern matrices, and smaller on vocabulary and general knowledge. Measured against today's scales, an average person from 1900 would score far below 100.
Why it happened
Because it happened within a few generations, the cause has to be environmental, not genetic. The usual explanations are:
- better nutrition and health, including less childhood illness
- more and longer schooling
- smaller families, with more attention per child
- daily life that asks for more abstract thinking: classifying, hypotheticals, working with symbols
- more familiarity with test-style tasks
Is it reversing?
Since the 1990s, scores have levelled off or slightly fallen in some countries, including Norway, Denmark and Finland. A study of Norwegian army records found the drop shows up even between brothers in the same family, which again points to environmental causes, such as changes in education, reading habits or the tests themselves, rather than genes.
What it means for you
Scores are always relative to the group a test was scaled on. An old test with out-of-date norms will make people look smarter than they are, which is one reason professional tests are re-scaled every 15 to 25 years.
Sources
- Flynn, J. R. (1984). The mean IQ of Americans: Massive gains 1932 to 1978. Psychological Bulletin, 95(1).
- Flynn, J. R. (1987). Massive IQ gains in 14 nations: What IQ tests really measure. Psychological Bulletin, 101(2).
- Pietschnig, J. & Voracek, M. (2015). One century of global IQ gains. Perspectives on Psychological Science, 10(3).
- Bratsberg, B. & Rogeberg, O. (2018). Flynn effect and its reversal are both environmentally caused. PNAS, 115(26).