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Flynn effect

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The Flynn effect is the increase of the average intelligence quotient (IQ) test scores over generations (IQ gains over time). The effect has also been reported for other cognitions such as semantic and episodic memory.[1] The effect occurs in most parts of the world although at greatly varying rates.

The Flynn effect is named for James R. Flynn, who did much to document it and promote awareness of its implications. However, the first to invent the term was not Flynn himself but the authors of The Bell Curve.[2]

The effect increase has been continuous and approximately linear from the earliest years of testing to the present. "Test scores are certainly going up all over the world, but whether intelligence itself has risen remains controversial," psychologist Ulric Neisser wrote in an article during 1997 in The American Scientist.[3] The Flynn effect may have ended in some developed nations starting during the mid 1990s although other studies, such as Black Americans reduce the racial IQ gap: Evidence from standardization samples (Dickens, Flynn; 2006), still show gains between 1972 and 2002.


The rise

IQ tests are re-normalized periodically, in order to maintain the average score for an age group at 100. In fact, the necessity for this re-normalization provided Flynn with an initial indication that IQ was 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.[3] 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.[3]

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.[4] However, Raven (2000) found that, as Flynn suggested, data reported by many previous researchers that had previously been interpreted as showing a decrease of 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.[5] Two large samples of Spanish children were assessed with a 30-year gap. Comparison of the IQ distributions indicated that

  1. the mean IQ 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.[6]
Possible projection of Flynn through Ages by Hugues CREPIN

If accepted at face value, these changes are considered large by some. 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.[3] In other words, half of the children of 1932 would be classified as having borderline mental retardation or worse during 1997. Considering Ravens, Neisser estimates that if you extrapolate 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 beyond the data leads to results such as an IQ of -1000 for Aristotle (even assuming he would have scored 200 in his day).[7]

Though the effect is most associated with IQ increases, a similar effect has been found with increases of semantic and episodic memory.[1]

Proposed explanations

See also: Health and intelligence

Attempted explanations have included improved nutrition, a trend towards smaller families, better education, greater environmental complexity, and heterosis[8]. 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.[3] Mathematics has been proposed as particularly important.[9]

Many studies find that children who do not attend school for one reason or another 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 5 or 6 points by doing so. 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.[3]

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 (age 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 twelve. Not all such projects have been successful.[3] Also, such IQ gains can diminish until the age of 18.[10] Several other studies have also found lasting cognitive gains.[11]

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, since 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."[3]

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. He 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 say that you 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, almost certainly 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.[6] 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 can not typically explain the Flynn Effect because it is 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.[12]

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.[3]. 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 increases of intelligence 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.[3]

Dickens and Flynn during 2001 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 can 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 would be most likely to produce long-term IQ gains if they taught children how to replicate outside the program the kinds of cognitively demanding experiences that produce IQ gains while they are in the program and motivate them to persist in that replication long after they have left the program.[13][14] However if the Flynn Effect is caused by intellectual stimulation, this may suggest that the Flynn Effect is unrelated to g[dubious – discuss] 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[15] ...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."[16] 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.[dubious – discuss]

Some researchers, such as J. Phillipe Rushton[17] argue the Flynn effect largely has not changed the general intelligence factor (g), which would mean the practical significance of the effect would be limited. More recent studies have found that g has improved substantially[18][19]

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, according to this study, some of the inter-generational difference of IQ is attributable to bias or other artifacts, and not real gains of general intelligence or higher-order ability factors.[20]

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.[21]

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.[22]

In conclusion a number of varied phenomena may be contributing to the Flynn effect.

Has progression ended?

William T. Dickens and James R. Flynn write that blacks have gained 5 or 6 IQ points as compared to non-Hispanic whites between 1972 and 2002. This graph shows the gains for various tests.[23]

The Flynn effect may have ended in some developed nations starting during the mid 1990s. In the United Kingdom amongst teenagers, it maximized during the 1980s and has since remained the same.[24]

Teasdale & 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."[25]

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 subtests, declined.[26]

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 downwards. However, even if there is a decrease, then 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.[9] 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.[27]

Also, if the Flynn effect has ended for the majority, it may still continue for minorities, especially for groups like immigrants where many may received poor nutrition during early childhood.[25] For example, William T. Dickens and James R. Flynn write in their 2006 paper Black Americans reduce the racial IQ gap: Evidence from standardization samples that blacks have gained 5 or 6 IQ points compared to non-Hispanic whites between 1972 and 2002. Gains have been fairly uniform across the entire range of black cognitive ability.[23] J. Philippe Rushton and Arthur R. Jensen have disputed their findings, calculating a mean gain for Blacks of 0 to 3.44 IQ points, and questioned the exclusion of four independent tests that showed low or negative IQ gains.[28]

The social multiplier effect

The primary causative agent of the Flynn effect is believed to be 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).[29] The reality of the effect has been challenged, however, most notably by Mingroni, who posits 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.[30]

See also

References

  1. ^ a b 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.2009.05.001 PMID 19056409
  2. ^ Flynn, J. R., 2007, page 2.
  3. ^ a b c d e f g h i j Rising Scores on Intelligence Tests Neisser, U. (1997). American Scientist, 85, 440-447.
  4. ^ Teasdale, Thomas W., and David R. Owen. (1987). ‘National secular trends in intelligence and education: a twenty year cross-sectional study’, Nature, 325, 119-21.
  5. ^ Raven, J. (2000). The Raven’s Progressive Matrices: Change and stability over culture and time. Cognitive Psychology, 41, 1-48.
  6. ^ a b 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)
  7. ^ The g factor, by Arthur Jensen pg 328
  8. ^ 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.
  9. ^ a b Rising mean IQ: Cognitive demand of mathematics education for young children, population exposure to formal schooling, and the neurobiology of the prefrontal cortex Clancy Blair, David Gamson, Steven Thorne, David Baker. Intelligence 33 (2005) 93-106
  10. ^ Plomin, R., DeFries, J. C., Craig, I. W., & McGuffin, P. (2003). Behavioral genetics in the postgenomic era. 4th Ed.
  11. ^ Contributions of early childhood education to age-14 performance Cathy Wylie, Edith Hodgen, Hilary Ferral, and Jean Thompson. NEW ZEALAND COUNCIL FOR EDUCATIONAL RESEARCH TE RÜNANGA O AOTEAROA MÖ TE RANGAHAU I TE MÄTAURANGA WELLINGTON 2006
  12. ^ "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.
  13. ^ William T. Dickens and James R. Flynn, Heritability Estimates Versus Large Environmental Effects:The IQ Paradox Resolved, Psychological Review 2001. Vol. 108, No. 2. 346-369.
  14. ^ William T. Dickens and James R. Flynn, "The IQ Paradox: Still Resolved," Psychological Review 109, no. 4 (2002).
  15. ^ The g factor by Arthur Jensen pg 336
  16. ^ The g factor by Arthur Jensen pg 344
  17. ^ 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.
  18. ^ 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}}: External link in |title= (help)CS1 maint: multiple names: authors list (link)
  19. ^ Colom R & Garcia-Lopez O (2003). "Secular Gains in Fluid Intelligence: Evidence from the Culture-Fair Intelligence Test". Journal of Biosocial Science. 35: 33–39. doi:10.1017/S0021932003000336. {{cite journal}}: External link in |title= (help)
  20. ^ 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) (links to PDF file)
  21. ^ Daley TC, Whaley SE, Sigman MD, Espinosa MP & Neumann C. "Iq on the rise: The Flynn Effect in Rural Kenyan Children". Psychological Science. 14 (3): 215–219. doi:10.1111/1467-9280.02434/abs/+Iq+on+the+rise:+The+Flynn+Effect+in+Rural+Kenyan+Children]. {{cite journal}}: External link in |title= (help)CS1 maint: multiple names: authors list (link)
  22. ^ 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. {{cite journal}}: External link in |title= (help)CS1 maint: multiple names: authors list (link)
  23. ^ a b Black Americans reduce the racial IQ gap: Evidence from standardization samples William T. Dickens and James R. Flynn. Oct. 2006
  24. ^ British teenagers have lower IQs than their counterparts did 30 years ago. The Telegraph. Feb 7, 2009.
  25. ^ a b 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.
  26. ^ Sundet, J (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.
  27. ^ Boyles, Salynn (November 7, 2006). "A 'Silent Pandemic' Of Brain Disorders". CBS News. Retrieved 2008-03-23.
  28. ^ 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)
  29. ^ Dickens, W. T., & Flynn, J. R. (2001). Heritability estimates versus large environmental effects: The IQ paradox resolved. Psychological Review, 108, 346-369.
  30. ^ Mingroni, M. A. (2007). Resolving the IQ paradox: Heterosis as a cause of the Flynn effect and other trends. Psychological Review, 114, 806-829.

Further reading

  • Flynn, J. R. (1984). The mean IQ of Americans: Massive gains 1932 to 1978. Psychological Bulletin, 95, 29-51.
  • Flynn, J. R. (1987). Massive IQ gains in 14 nations: What IQ tests really measure. Psychological Bulletin, 101, 171-191.
  • Flynn, J. R., What is Intelligence?: Beyond the Flynn Effect, Cambridge University Press (2007).
  • Ulric Neisser et al.: The Rising Curve: Long-Term Gains in IQ and Related Measures. American Psychological Association (APA), 1998, ISBN 1-55798-503-0.
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