What Is the Flynn Effect? Why Global IQ Rose — and Recently Stalled

It may sound surprising that people today score higher on IQ tests than people in the past. Yet intelligence research has repeatedly confirmed that average IQ test scores rose across countries throughout the 20th century. This is the Flynn effect.

What is the Flynn effect?

The phenomenon is best known from the systematic work of political scientist James Flynn in the 1980s: comparing standardization data across countries, raw IQ scores were rising at a pace of roughly 3 points per decade. The reason the average IQ is always 100 is that the yardstick is periodically rebuilt (restandardization) — meaning the yardstick itself has been revised upward again and again. For the basics of the mean-100, SD-15 system, see our explanation of the average IQ and its distribution.

Why did scores rise? The leading explanations

There is no single cause; a combination of factors is thought to be at work: improved nutrition and health, longer schooling, smaller families, and society as a whole becoming accustomed to "test-like" thinking with figures, symbols, and hypotheticals (Flynn himself described it as putting on "scientific spectacles"). Intriguingly, the gains were larger not on knowledge questions but on fluid-intelligence tasks such as matrix reasoning — spotting rules on the spot. Fluid intelligence is covered in the difference between fluid and crystallized intelligence.

The recent stall and the "reverse Flynn effect"

Since the 1990s, some developed countries — Norway and Denmark among them — have reported a stall in the rise, and even a gradual decline (the reverse Flynn effect). Candidate explanations include changes in education, test motivation, and environmental factors, but nothing is settled. At minimum, the data show that IQ does not rise without limit.

What the Flynn effect teaches us

The phenomenon is regarded as powerful evidence that IQ scores are strongly influenced by environmental factors. Once changes equivalent to dozens of points occurred between generations, the difference cannot be explained by genetics alone. It is also a reminder that IQ is a relative measure whose meaning depends on when the yardstick was set. The difficulty of comparing national averages is covered in the limits of average IQ by country.

Know where you stand by today's standard

Modern IQ tests are calibrated against today's test takers, so your score reflects your position among your contemporaries. To find out where you stand now, check your estimated IQ, deviation score, and top percentile with the free IQ test.