What is the Flynn effect, and why do IQ scores keep rising?

The Flynn effect is the gradual, cross-cultural rise in raw scores on measures of general intelligence. The APA Dictionary of Psychology puts the gain at roughly 9 points per generation of 30 years. It is named after the New Zealand philosopher and researcher James Flynn, who documented it in the 1980s. [1] [2]

IQ tests are standardized on a sample of test-takers, with the average set to 100 and the standard deviation set to 15 or 16 points. When a test is revised, a new and usually more recent sample is used and the average is reset to 100. When those newer test-takers sit the older test, their average is almost always well above 100, according to Wikipedia's summary. [3]

Flynn's 1984 study of the standardization samples of successive Stanford-Binet and Wechsler tests found a 13.8-point rise between 1932 and 1978. That works out to about 0.3 points per year, or roughly 3 points per decade. The gains were uneven across abilities, with fluid abilities rising substantially more than crystallized ones. [4] [1]

A 2014 meta-analysis in Psychological Bulletin by Trahan and colleagues covered 285 studies since 1951 and found an average gain of 2.31 points per decade. For modern Stanford-Binet and Wechsler tests, normed since 1972, the figure was 2.93 points per decade, close to the common rule of thumb of 3. The authors found no support for the idea that the effect is shrinking, and they found it held across age groups, measures and ability levels. [4]

The effect has practical consequences. An older test overestimates a person's IQ by about 0.3 points for each year since it was normed. This matters in high-stakes decisions such as intellectual disability determinations in US death penalty cases, where whether to adjust for the Flynn effect is contested. [4]

Flynn himself concluded that the gains do not necessarily mean people are more intelligent in a general sense. He argued that ways of thinking changed with social conditions and technology, including longer schooling and more emphasis on abstract thinking and symbols, whereas earlier generations thought more concretely. EBSCO describes this as the view many researchers share. [2]

The exact causes remain disputed. Other researchers point to better nutrition, greater general environmental stimulation, and fewer infectious diseases. Wikipedia also lists more efficient education among the proposed explanations, and notes skepticism about what the gains imply. [2] [3]

Some studies, including work by Flynn and others, suggest scores have plateaued or declined in some developed countries since the 1990s or earlier, sometimes called the reverse Flynn effect. In some cases the apparent decline may reflect cultural change making parts of tests obsolete. The 2014 meta-analysis, by contrast, found no sign of diminishing gains in the studies it examined. [2] [3] [4]