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The Flynn effect is the increase in raw scores on IQ tests over time, also called secular change in IQ. When new norms are calculated for an IQ test, it is observed that the number of correct item content scores achieved by test-takers in the norming sample typically rise compared to test-takers in previous norming samples. Similar improvements have been reported for other cognitions such as semantic and episodic memory. The effect has been observed in most parts of the world at different rates. Because IQ 100 is defined as the median score of the norming sample, current test-takers taking tests with older norms tend to have inflated scores. The Flynn effect is named for James R. Flynn, who did much to document it and promote awareness of its implications. The term itself was coined by the authors of The Bell Curve. The effect's increase has been continuous and approximately linear from the earliest years of testing to the present. There are numerous proposed explanations of the Flynn effect and also some skepticism about its implications. The Flynn effect may have ended in at least a few developed nations, possibly allowing the national differences in IQ scores to diminish if the Flynn effects continues in nations with lower average national IQs.

The rise

IQ tests are re-normalized periodically, in order to maintain an average score at 100. In fact, the necessity of this re-normalization provided an early indication that IQ-scores on the test were changing over time. The revised versions are standardized on new samples and scored with respect to those samples alone, so the only way to compare the difficulty of two versions of a test is to conduct a separate study in which the same subjects take both versions. Doing so confirms IQ gains over time.

The average rate of increase seems to be about three IQ points per decade. 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. The greatest Flynn effects occur instead for general intelligence factor loaded (g-loaded) tests such as Raven's Progressive Matrices. For example, Dutch conscripts gained 21 points during only 30 years, or 7 points per decade, between 1952 and 1982.

Some studies emphasizing the distribution of scores have found the Flynn effect to be primarily a phenomenon of the lower end of the distribution. Teasdale and Owen (1987), 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. However, 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 date of birth. On many tests this occurs at all levels of ability. Two large samples of Spanish children were assessed with a 30-year gap. Comparison of the IQ distributions indicated that

  1. the mean IQ-scores on the test had increased by 9.7 points (the Flynn effect),
  2. the gains were concentrated in the lower half of the distribution and negligible in the top half, and
  3. the gains gradually decreased as the IQ of the individuals increased.

Psychologist Ulric Neisser, who, during 1995, headed an American Psychological Association task force writing a consensus statement on the state of intelligence research, estimates that if American children of 1932 could take an IQ test normed during 1997 their average IQ would have been only about 80, which would be classified as between low average and borderline retarded. Neisser stated: "Test scores are certainly going up all over the world, but whether intelligence itself has risen remains controversial." Considering Ravens, Neisser estimates that if he extrapolates beyond the data, which shows a 21-point gain between 1952 and 1982, an even larger gain of 35 IQ points can be argued. However Arthur Jensen warns that extrapolating leads to results such as an IQ of -1000 for Aristotle (even assuming he would have scored 200 in his day).


Though the effect is most associated with IQ increases, a similar effect has been found with increases of semantic and episodic memory.

Proposed explanations

See also: Health and intelligence

Attempted explanations have included improved nutrition, a trend toward smaller families, better education, greater environmental complexity, and heterosis. Another proposition is greater familiarity with multiple-choice questions and experience with brain-teaser IQ problems.

Duration of average schooling has increased steadily. One problem with this explanation is that if comparing older and more recent subjects with similar educational levels, then the IQ gains appear almost undiminished in each such group considered individually. Mathematics has been proposed as particularly important.

Many studies find that children who do not attend school score 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 Caucasian children. On average, the scores of African-American children who did not receive formal education during that period decreased at a rate of about six IQ points per year.

Another explanation is an increased familiarity of the general population with tests and testing. For example, children who take the very same IQ test a second time usually gain five or six points. However, this seems to set an upper limit on the effects of test sophistication. One problem with this explanation and other related to the schooling is, as noted above, that those subsets one would expect to be affected the most show the least increases.

Another theory is that many parents are now interested in their children's intellectual development and are probably doing more to encourage it than parents did in the past. 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 difference between the groups, although only five points, was still present at age 12. Not all such projects have been successful. Also, such IQ gains can diminish until age 18. Several other studies have also found lasting cognitive gains.

Still another theory is that the general environment today is much more complex and stimulating. One of the most striking 20th century changes of the human intellectual environment has come from the increase of exposure to many types of visual media. From pictures on the wall to movies to television to video games to computers, each successive generation has been exposed to richer optical displays than the one before and may have become more adept at visual analysis. This would explain why tests like the Raven's have shown the greatest increases—they depend on such analysis. This explanation may imply that IQ tests do not necessarily measure a general intelligence factor, especially not Raven's as often argued, but instead may measure different types of intelligence that are developed by different experiences (this argument is against the notion of an underlying general intelligence, or g factor). An increase only of particular form(s) of intelligence would explain why the Flynn effect has not caused a "cultural renaissance too great to be overlooked."

Related to this, James Flynn's current explanation (Flynn 2007) is that environmental changes resulting from modernization—such as more intellectually demanding work, greater use of technology and smaller families—have meant that a much larger proportion of people are more accustomed to manipulating abstract concepts such as hypotheses and categories than a century ago. Substantial portions of IQ tests deal with these abilities. Flynn gives, as an example, the question 'What do a dog and a rabbit have in common?' A modern respondent might say they are both mammals (an abstract answer), whereas someone a century ago might have said that humans catch rabbits with dogs (a concrete answer).

Improved nutrition is another explanation. Today's average adult from an industrialized nation is taller than a comparable adult of a century ago. That increase of stature, likely the result of general improvements of nutrition and health, has been at a rate of more than a centimeter per decade. Available data suggest that these gains have been accompanied by analogous increases of head size, and presumably by an increase of the average size of the brain. This argument has the difficulty that groups who tend to be of smaller overall body size (e.g. women, people of Asian ancestry) do not show lower average IQs.

A 2005 study presented data supporting the nutrition hypothesis, which predicts that gains of IQ will occur predominantly at the low end of the distribution where nutritional deprivation is (was) most severe. Richard Lynn first proposed the nutrition hypothesis and defends it as the only plausible explanation for the Flynn effect in most samples. Lynn argues that cultural factors cannot typically explain the Flynn effect because its gains are observed even with infant development tests, thus nutrition at the earliest stages of life is the best explanation.

Possibly related to the Flynn effect is change of cranial vault size and shape during the last 150 years in the US. These changes must occur by early childhood because of the early development of the vault.

Another explanation for the Flynn effect is that is caused by the social multiplier effect. This effect is based on the idea that the ambient cognitive background of societies passively increases IQ by the provision of iteratively more complex forms of environmental stimulus (such as improvements of media, technology and nutrition). The reality of the effect has been challenged, however, most notably by Mingroni, who says that the heritability of g is too great to be affected significantly by environmental factors. Mingroni has proposed heterosis (hybrid vigor associated with historical reductions of the levels of inbreeding) as an alternative explanation of the Flynn effect as it pertains to increases of g.

Flynn argued earlier that the very large increase indicates that IQ tests do not measure intelligence well but only a minor sort of "abstract problem-solving ability" with little practical significance. This refers to the validity of IQ tests and whether they assess something akin to most people's everyday understanding of "intelligence". Some have argued that if IQ gains do reflect intelligence increases in this sense, there would have been consequent changes of our society that have not been observed (given the presumed non-occurrence of the "cultural renaissance" referred to above).

In 2001, Dickens and Flynn presented a model for resolving several contradictory findings regarding IQ. They argue that the measure "heritability" includes both a direct effect of the genotype on IQ and also indirect effects such that the genotype changes the environment, thereby affecting IQ. That is, those with a greater IQ tend to seek stimulating environments that further increase IQ. These reciprocal effects result in gene environment correlation. The direct effect could initially have been very small but feedback can create large differences of IQ. In their model, an environmental stimulus can have a very great effect on IQ, even for adults, but this effect also decays over time unless the stimulus continues (the model could be adapted to include possible factors, like nutrition during early childhood, that may cause permanent effects). The Flynn effect can be explained by a generally more stimulating environment for all people. The authors suggest that programs intending to increase IQ may produce long-term IQ gains if the programs taught children how to replicate the types of cognitively demanding experiences that produce IQ gains outside the program. To maximize lifetime IQ, the programs should also motivate them to continue searching for cognitively demanding experiences after they have left the program.

However if the Flynn effect is caused by intellectual stimulation, this may suggest that the Flynn effect is unrelated to g because according to Jensen "the preponderance of evidence argues that variance in the level of g is not a psychologically manipulable variable, but rather a biological phenomenon under the control both of the genes and of those external physical variables that affect the physiological and biochemical functioning of the central nervous system, which mediates the behavioral manifestations of g ...Anything less than very early and intensive intervention, including medical and nutritional advances, during the preschool years (and also prenatally) is probably inadequate to cause a lasting increase in the child's level of g." However, Dickens and Flynn's paper, which was written after Jensen's book, disputes Jensen's claims, for example arguing that using Jensen's method the Flynn effect is found to be substantially due to genetic improvements, an extremely unlikely cause.

Some studies indicate that the Flynn effect has not substantially affected the general intelligence factor (g), which would mean that the practical significance of the effect would be limited. However, a Dutch study found g gains in descendants of non-Western immigrants, while another study found g gains in Spanish students.

Studies that use multi-group confirmatory factor analysis test for "measurement invariance". Where tenable, invariance demonstrates that group differences exist in the latent constructs the tests contain and not, for example, as a result of measurement artifacts or cultural bias. Wicherts et al. (2004) found evidence from five data sets that IQ scores are not measurement invariant over time, and thus "the gains cannot be explained solely by increases at the level of the latent variables (common factors), which IQ tests purport to measure". In other words, some of the inter-generational differences of IQ are attributable to bias or other artifacts, and not real gains of general intelligence or higher-order ability factors.

A 2003 study looking at the Flynn effect in Kenya between 1984 and 1998 found that the increase was best explained by parents' literacy, family structure, and children's nutrition and health.

A 2006 study from Brazil examined data from testing children during 1930 and 2002–2004, the largest time gap ever considered. The results are consistent with both the cognitive stimulation and the nutritional hypotheses.

Possible end of progression

William T. Dickens and James R. Flynn write that black Americans have gained five or six IQ points as compared to non-Hispanic whites between 1972 and 2002. This graph shows the gains for various tests.

The Flynn effect may have ended in some developed nations starting during the mid-1990s. In the United Kingdom among teenagers, IQ maximized during the 1980s and has since reversed marginally.

Teasdale and Owen (2005) "report intelligence test results from over 500,000 young Danish men, tested between 1959 and 2004, showing that performance peaked in the late 1990s, and has since declined moderately to pre-1991 levels". They speculate that "a contributing factor in this recent fall could be a simultaneous decline in proportions of students entering 3-year advanced-level school programs for 16–18 year olds."

During 2004, Jon Martin Sundet of the University of Oslo and colleagues published an article documenting scores on intelligence tests given to Norwegian conscripts between the 1950s and 2002, showing that the increase of scores of general intelligence stopped after the mid-1990s and in numerical reasoning sub-tests, declined.

Some have claimed that the Flynn effect was masking a dysgenic decrease of human reproduction and that in developed countries the only direction that IQ scores will now trend is downward. However, even if there is a decrease, this may have causes other than dysgenics. Genetic changes usually happen relatively slowly. For example, the Flynn effect has been too rapid for a genetic explanation. Researchers have warned that constantly greater exposure to industrial chemicals proven to damage the nervous system, especially in children, in industrialized nations may be responsible for a "silent pandemic" of brain development disorders.

Also, if the Flynn effect has ended for the majority, it may still continue for minorities, especially for groups like immigrants where many may have received poor nutrition during early childhood.

Dickens and Flynn write in their 2006 paper Black Americans reduce the racial IQ gap: Evidence from standardization samples that blacks have gained five or six IQ points compared to non-Hispanic whites between 1972 and 2002. Gains have been fairly uniform across the entire range of black cognitive ability. J. Philippe Rushton and Arthur R. Jensen have disputed Dickens's and Flynn's findings, calculating a mean gain for Blacks of zero to 3.44 IQ points, and questioned the exclusion of four independent tests that showed low or negative IQ gains. However, in the very same 2006 study that was criticized by Rushton and Jensen, Flynn and Dickens give explicit reasons for why four tests were excluded. Rushton and Jensen include in test such as the AFQT which is not strictly an IQ tests and their inclusion of Herrnstein and Murray's AFQT data was criticized by Flynn and Dickens. Rushton and Jensen derive the figure of a 3.44 IQ point gain by adding data from four excludes tests to Table A1 while Flynn and Dickens' figure of a 5.5 IQ gain for black Americans was derived from Figure 3 in the study.

Teasdale and Owen (2007), in a study on young adult males in Denmark, found that there was a modest increase between 1988 and 1998, but a modest decrease between 1998 and 2003/2004. The difference was approximately 1.5 IQ points in both cases. A partial contributing factor to the recent decline may the rising proportion of immigrants or their immediate descendants in Denmark. This is supported by data on Danish draftees where first or second generation immigrants with Danish nationality score below average. They also state that since the Flynn effect may thus have ended in at least a few developed nations, this may possibly allowing the national differences in IQ scores (see IQ and Global Inequality) to diminish if the Flynn effects continues in nations with lower average national IQs.

See also

References

  1. ^ Rönnlund M, Nilsson LG (2009). "Flynn effects on sub-factors of episodic and semantic memory: parallel gains over time and the same set of determining factors". Neuropsychologia. 47 (11): 2174–80. doi:10.1016/j.neuropsychologia.2008.11.007. PMID 19056409. {{cite journal}}: Unknown parameter |month= ignored (help)
  2. Flynn, James R. (2009). What Is Intelligence: Beyond the Flynn Effect (expanded paperback ed.). Cambridge: Cambridge University Press. pp. 1–2. ISBN 978-0-521-74147-7. The 'Flynn effect' is the name that has become attached to an exciting development, namely, that the twentieth century saw massive IQ gains from one generation to another. To forestall a diagnosis of megalomania, the label was coined by Herrnstein and Murray, the authors of The bell curve, and not by myself. {{cite book}}: Invalid |ref=harv (help); Unknown parameter |laydate= ignored (help); Unknown parameter |laysummary= ignored (help)
  3. ^ Teasdale TW, Owen DR (2008). "Secular declines in cognitive test scores: A reversal of the Flynn Effect" (PDF). Intelligence. 36 (2): 121–6. doi:10.1016/j.intell.2007.01.007.
  4. ^ Neisser U (1997). "Rising Scores on Intelligence Tests". American Scientist. 85: 440–7.
  5. Teasdale TW, Owen DR (1987). "National secular trends in intelligence and education: a twenty year cross-sectional study". Nature. 325: 119–21. doi:10.1038/325119a0.
  6. Raven J (2000). "The Raven's Progressive Matrices: Change and stability over culture and time". Cognitive Psychology. 41 (1): 1–48. doi:10.1006/cogp.1999.0735. PMID 10945921.
  7. ^ Colom, R., Lluis-Font, J.M., and Andrés-Pueyo, A. (2005). "The generational intelligence gains are caused by decreasing variance in the lower half of the distribution: Supporting evidence for the nutrition hypothesis". Intelligence. 33: 83–91. doi:10.1016/j.intell.2004.07.010.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  8. http://webspace.ship.edu/cgboer/intelligence.html
  9. The g factor, by Arthur Jensen pg 328
  10. Mingroni, M.A. (2004). "The secular rise in IQ: Giving heterosis a closer look". Intelligence. 32: 65–83. doi:10.1016/S0160-2896(03)00058-8.
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  12. Plomin, R., DeFries, J. C., Craig, I. W., & McGuffin, P. (2003). Behavioral genetics in the postgenomic era. 4th Ed.
  13. Cathy Wylie, Edith Hodgen, Hilary Ferral, and Jean Thompson (2006). "Contributions of early childhood education to age-14 performance" (PDF). Wellington: New Zealand Council for Educational Research Te Rünanga O Aotearoa Mö Te Rangahau I Te Mätauranga.{{cite web}}: CS1 maint: multiple names: authors list (link)
  14. "Changes in vault dimensions must occur by early childhood because of the early development of the vault." Secular change in craniofacial morphology "During the 125 years under consideration, cranial vaults have become markedly higher, somewhat narrower, with narrower faces. The changes in cranial morphology are probably in large part due to changes in growth at the cranial base due to improved environmental conditions. The changes are likely a combination of phenotypic plasticity and genetic changes over this period." Cranial change in Americans: 1850-1975.
  15. ^ Dickens WT, Flynn JR (2001). "Heritability estimates versus large environmental effects: The IQ paradox resolved". Psychological Review. 108 (2): 346–369. doi:10.1037/0033-295X.108.2.346. PMID 11381833.
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  17. Dickens WT, Flynn JR (2002). "The IQ Paradox: Still Resolved" (PDF). Psychological Review. 109 (4).
  18. The g factor by Arthur Jensen pg 336
  19. The g factor by Arthur Jensen pg 344
  20. Rushton, J. P. (1999). "Secular Gains in IQ Not Related to the g Factor and Inbreeding Depression—Unlike Black-White Differences: A Reply to Flynn" (PDF). Personality and Individual Difference. 26: 381–389. doi:10.1016/S0191-8869(98)00148-2.
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  22. Rushton, J. P. and Jensen, A. (2010). "The rise and fall of the Flynn effect as a reason to expect a narrowing of the Black–White IQ gap". Intelligence. 38: 213–9. doi:10.1016/j.intell.2009.12.002.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  23. Te Nijenhuis J, De Jong M-J, Evers A, Van Der Flier H. (2004). "Are cognitive differences between immigrant and majority groups diminishing?". European Journal of Personality. 18 (5): 405–434. doi:10.1002/per.511.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  24. Colom R & Garcia-Lopez O (2003). "Secular Gains in Fluid Intelligence: Evidence from the Culture-Fair Intelligence Test". Journal of Biosocial Science. 35 (1): 33–9. doi:10.1017/S0021932003000336. PMID 12537154.
  25. Wicherts, J.M., Dolan, C.V., Hessen, D.J., Oosterveld, P., Baal, G.C.M. van, Boomsma, D.I., & Span, M.M. (2004). "Are intelligence tests measurement invariant over time? Investigating the nature of the Flynn effect" (PDF). Intelligence. 32: 509–537. doi:10.1016/j.intell.2004.07.002.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  26. Daley TC, Whaley SE, Sigman MD, Espinosa MP & Neumann C (2003). "Iq on the rise: The Flynn Effect in Rural Kenyan Children". Psychological Science. 14 (3): 215–9. doi:10.1111/1467-9280.02434. PMID 12741743.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  27. Colom R, Flores-Mendoza CE, & Abad FJ (2007). "Generational changes on the draw-a-man test: a comparison of Brazilian urban and rural children tested in 1930, 2002 and 2004". J Biosoc Sci. 39 (1): 79–89. doi:10.1017/S0021932005001173. PMID 16441963.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  28. ^ William T. Dickens and James R. Flynn. (October 2006). "Black Americans reduce the racial IQ gap: Evidence from standardization samples" (PDF).
  29. Gray, Richard (February 7, 2009). "British teenagers have lower IQs than their counterparts did 30 years ago". London: The Telegraph.
  30. Teasdale TW & Owen DR (2005). "A long-term rise and recent decline in intelligence test performance: The Flynn Effect in reverse". Personality and Individual Differences. 39 (4): 837–843. doi:10.1016/j.paid.2005.01.029.
  31. Sundet, J; Barlaug, D; Torjussen, T (2004). "The end of the Flynn Effect. A study of secular trends in mean intelligence scores of Norwegian conscripts during half a century". Intelligence. 32: 349. doi:10.1016/j.intell.2004.06.004.
  32. Boyles, Salynn (November 7, 2006). "A 'Silent Pandemic' Of Brain Disorders". CBS News. Retrieved 2008-03-23.
  33. Rushton JP, Jensen AR (2006). "The Totality of Available Evidence Shows the Race IQ Gap Still Remains" (PDF). Psychological Science. 19 (10): 921–922. doi:10.1111/j.1467-9280.2006.01803.x. PMID 17100794. {{cite journal}}: Unknown parameter |month= ignored (help)
  34. Black Americans Reduce the Racial IQ Gap: Evidence from Standardization Samples Forthcoming: Psychological Science, October 2006 By William T. Dickens1 & James R. Flynn. pg. 9

Further reading

  • Flynn, J. R. (1984). "The mean IQ of Americans: Massive gains 1932 to 1978". Psychological Bulletin. 95: 29–51. doi:10.1037/0033-2909.95.1.29.
  • Flynn, J. R. (1987). "Massive IQ gains in 14 nations: What IQ tests really measure". Psychological Bulletin. 101: 171–191. doi:10.1037/0033-2909.101.2.171.
  • Flynn, J. R. (2007). What is Intelligence?: Beyond the Flynn Effect. Cambridge University Press. ISBN 0521880076.
  • Ulric Neisser; et al. (1998). The Rising Curve: Long-Term Gains in IQ and Related Measures. American Psychological Association (APA). ISBN 1-55798-503-0. {{cite book}}: Explicit use of et al. in: |author= (help)

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