Flynn Effect

Evidence for the Flynn Effect

There is a lot of documented evidence to support the increasing trend in IQ scores both in industrialized and third-world countries. For example, the United States had a gain of 14 IQ points from 1932 to 1978, Estonia had a 12-point gain from 1933 to 2006, Japan had a 19-point gain from 1940 to 1965, and Argentina had a 21-point gain from 1964 to 1998. IQ gains have been robust across intelligence test batteries, ages, and ability levels. Although IQ gains have been found with an overall positive trend line, the rate in gains has varied by country, time period, and test type (e.g., scholastic vs. nonscholastic). Furthermore, the magnitude of gains has varied; and in some cases, the Flynn effect phenomenon has tapered off in a few developed nations, narrowing the gap in national IQ score differences between countries.

Why the Flynn Effect Happens

Numerous hypotheses have been advanced to explain the phenomenon of IQ score increases observed over time. Some explanations include improved nutrition, better education, greater environmental complexity, or even increases in test-taking skills. However, one drawback to the improvement in test-taking skills hypothesis is that those subtests most affected by improvements demonstrate the smallest gains. Researchers have noted that IQ score gains have occurred within too small of a time frame for genetic selection to be the cause. Another potential cause of IQ score gains over time may simply be due to artifacts of measurement differences. When comparing IQ test scores across different age cohorts, the measurement of the intended construct may vary by cohort, an issue of measurement invariance. In fact, researchers have found support to suggest that differences in measurement, not differences in true IQ, have explained the Flynn effect. Further, tests based on classical test theory versus item response theory may inhibit our understanding of gains in IQ scores. Specifically, tests based on classical test theory could show score differences in different normed versions of tests, but the differences are confounded by the fact that the difference may be due to a decreased level of difficulty in the test items, not a difference in true gains or in raw intelligence. This issue is typically resolved through the use of item response theory, as item properties can be taken into account. In general, researchers postulate that it may be some combination of factors at different times that have explained increases in IQ scores.

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