The Flynn effect is the substantial and long-sustained increase in both fluid and crystallized intelligence test scores that were measured in many parts of the world over the 20th century, named after researcher James Flynn (1934–2020). When intelligence quotient (IQ) tests are initially standardized using a sample of test-takers, by convention the average of the test results is set to 100 and their standard deviation is set to 15 or 16 IQ points. When IQ tests are revised, they are again standardized using a new sample of test-takers, usually born more recently than the first; the average result is set to 100. When the new test subjects take the older tests, in almost every case their average scores are significantly above 100.
Test score increases have been continuous and approximately linear from the earliest years of testing to the present. For example, a study published in the year 2009 found that British children's average scores on the Raven's Progressive Matrices test rose by 14 IQ points from 1942 to 2008. Similar gains have been observed in many other countries in which IQ testing has long been widely used, including other Western European countries, as well as Japan and South Korea. Improvements have also been reported for semantic and episodic memory.
There are numerous proposed explanations of the Flynn effect, such as the rise in efficiency of education, along with skepticism concerning its implications. Some researchers have suggested the possibility of a mild reversal in the Flynn effect (i.e., a decline in IQ scores) in developed countries, beginning in the 1990s, sometimes referred to as reverse Flynn effect. In certain cases, this apparent reversal may be due to cultural changes rendering parts of intelligence tests obsolete. However, as of the mid-2010s, meta-analyses indicated that, overall, the Flynn effect continued, either at the same rate, or at a slower rate in developed countries.
Origin of term
The Flynn effect is named for James Robert Flynn, who did much to document it and promote awareness of its implications. The term was coined by Richard Herrnstein and Charles Murray in their 1994 book The Bell Curve. Flynn stated that, if asked, he would have named the effect after Read D. Tuddenham who "was the first to present convincing evidence of massive gains on mental tests using a nationwide sample" in a 1948 article.
Although the general term for the phenomenon—referring to no researcher in particular—continues to be "secular rise in IQ scores", many textbooks on psychology and IQ testing have now followed the lead of Herrnstein and Murray in calling the phenomenon the Flynn effect.
Rise in IQ during the 20th century IQ tests are updated periodically. For example, the Wechsler Intelligence Scale for Children (WISC), originally developed in 1949, was updated in 1974, 1991, 2003, and again in 2014. The revised versions are standardized based on the performance of test-takers in standardization samples. A standard score of IQ 100 is defined as the mean performance of the standardization sample. Thus one way to see changes in norms over time is to conduct a study in which the same test-takers take both an old and new version of the same test. Doing so confirms IQ gains over time. Some IQ tests—for example, tests used for military draftees in NATO countries in Europe—report raw scores, and those also confirm a trend of rising scores over time. The average rate of increase seems to be about three IQ points per decade in the United States, as scaled by the Wechsler tests. The increasing test performance over time appears on every major test, in every age range, at every ability level, and in every modern industrialized country, although not necessarily at the same rate as in the United States. The increase was continuous and roughly linear from the earliest days of testing to the mid-1990s. Though the effect is most associated with IQ increases, a similar effect has been found with increases in attention and of semantic and episodic memory.
Ulric Neisser estimated that using the IQ values of 1997, the average IQ of the United States in 1932, according to the first Stanford–Binet Intelligence Scales standardization sample, was 80. Neisser states that "Hardly any of them would have scored 'very superior', but nearly one-quarter would have appeared to be 'deficient.'" He also wrote that "Test scores are certainly going up all over the world, but whether intelligence itself has risen remains controversial." Quantitative psychologist, Joseph Lee Rodgers argues that the effect occurs outside of families in any case.Joseph Lee Rodgers (2014). "http://www.iapsych.com/iqmr/fe/LinkedDocuments/rodgers2014.pdf Intelligence Are birth order effects on intelligence really Flynn Effects? Reinterpreting Belmont and Marolla 40 years later" (PDF). Intelligence 42: 128-133. "No within-family data exist that document an increase in intelligence over birth order, suggesting that its source derives from outside the family and will only manifest in data and analyses that account for between-family variance (such as cross-sectional data)." (p. 130)
Trahan et al. (2014) found that the effect was about 2.93 points per decade, based on both Stanford–Binet and Wechsler tests; they also found no evidence the effect was diminishing. In contrast, Pietschnig and Voracek (2015) reported, in their meta-analysis of studies involving nearly 4 million participants, that the Flynn effect had decreased in recent decades. They also reported that the magnitude of the effect was different for different types of intelligence ("0.41, 0.30, 0.28, and 0.21 IQ points annually for fluid, spatial, full-scale, and crystallized IQ test performance, respectively"), and that the effect was stronger for adults than for children.
Raven (2000) found that, as Flynn suggested, data interpreted as showing a decrease in many abilities with increasing age must be re-interpreted as showing that there has been a dramatic increase of these abilities with the date of birth. On many tests this occurs at all levels of ability.
Some studies have found the gains of the Flynn effect to be particularly concentrated at the lower end of the distribution. Teasdale and Owen (1989), for example, found the effect primarily reduced the number of low-end scores, resulting in an increased number of moderately high scores, with no increase in very high scores. In another study, two large samples of Spanish children were assessed with a 30-year gap. Comparison of the IQ distributions indicated that the mean IQ scores on the test had increased by 9.7 points (the Flynn effect), the gains were concentrated in the lower half of the distribution and negligible in the top half, and the gains gradually decreased as the IQ of the individuals increased. Some studies have found a reverse Flynn effect with declining scores for those with high IQ.
In 1987, Flynn took the position that the very large increase indicates that IQ tests do not measure intelligence but only a minor sort of "abstract problem-solving ability" with little practical significance. He argued that if IQ gains did reflect intelligence increases, there would have been consequent changes of our society that have not been observed (a presumed non-occurrence of a "cultural renaissance"). By 2012 Flynn no longer endorsed this view of intelligence, having elaborated and refined his view of what rising IQ scores meant.
Precursors to Flynn's publications Earlier investigators had discovered rises in raw IQ test scores in some study populations, but had not published general investigations of that issue in particular. Historian Daniel C. Calhoun cited earlier psychology literature on IQ score trends in his book The Intelligence of a People (1973). Robert L. Thorndike – not to be confused with his famous father Edward – drew attention to rises in Stanford-Binet scores in a 1975 review of the history of intelligence testing. In 1982, Richard Lynn recorded an increase in average IQ among the population of Japan.
Intelligence
There is debate about whether the rise in IQ scores also corresponds to a rise in general intelligence, or only a rise in special skills related to taking IQ tests. Because children attend school longer now and have become much more familiar with the testing of school-related material, one might expect the greatest gains to occur on such school content-related tests as vocabulary, arithmetic or general information. Just the opposite is the case: abilities such as these have experienced relatively small gains and even occasional decreases over the years. Meta-analytic findings indicate that Flynn effects occur for tests assessing both fluid and crystallized abilities. For example, Dutch conscripts gained 21 points during only 30 years, or 7 points per decade, between 1952 and 1982. This rise in IQ test scores is not wholly explained by an increase in general intelligence. Studies have shown that while test scores have improved over time, the improvement is not fully correlated with latent factors related to intelligence. Other researchers argue that the IQ gains described by the Flynn effect are due in part to increasing intelligence, and in part to increases in test-specific skills. One study suggested that the IQ gains reflected changes in modes of thinking that better reflected cognitive skills assessed by IQ tests rather than raw intelligence itself.
Proposed explanations
Schooling The duration of average schooling has increased steadily. However, a criticism of this explanation is that if (in the United States) older and younger subjects, with similar educational levels, are compared together, then the IQ gains appear almost undiminished in each group compared to when they are considered individually.
Many studies find that children who do not attend school score drastically lower on the tests than their regularly attending peers. During the 1960s, when some Virginia counties closed their public schools to avoid racial integration, compensatory private schooling was available only for White children. On average, the scores of African-American children who received no formal education during that period decreased at a rate of about six IQ points per year.
Research led by Stuart Ritchie in 2018, a Scottish psychologist and science communicator at the University of Edinburgh known for his research in human intelligence, further supports that education improves cognitive abilities. Ritchie and his team reviewed nearly 30 studies involving some 600,000 people. These studies included broad longitudinal observational studies tracking individuals' intelligence scores at various points in their lives, natural experiments created when the mandatory number of years of schooling changed in different areas, and school admission-date cutoffs used to compare students whose birthdays led them to have an additional year of school compared to similar students with slightly later birthdates. From this extensive review, they concluded that there was consistent evidence that formal schooling increased IQ by between 1 and 5 points for each additional year of education and that formal schooling is the most consistent, robust, and durable method known for raising intelligence.
Early intervention programs have shown mixed results. Some preschool (ages 3–4) intervention programs like "Head Start" do not produce lasting changes of IQ, although they may confer other benefits. The "Abecedarian Early Intervention Project", an all-day program that provided various forms of environmental enrichment to children from infancy onward, showed IQ gains that did not diminish over time. The IQ gains in the experimental group compared to the control group was 4.4 points. These gains persisted until at least age 21.
Citing a high correlation between rising literacy rates and gains in IQ, David Marks has argued that the Flynn effect is caused by changes in literacy rates.