Flynn effect

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Origin of term[edit]

External video
Jim Flynn U of Otago.jpg
James Flynn: Why our IQ levels are higher than our grandparents', (18:41), TED talks

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 Richard Herrnstein and Charles Murray, authors of The Bell Curve.[5] 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.[6]

Rise in IQ[edit]


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."[7]

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.[8]



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 do 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").[7] Flynn no longer endorses this view of intelligence and has since elaborated and refined his view of what rising IQ scores mean.

Precursors to Flynn's publications[edit]

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).[12] R. L. Thorndike drew attention to rises in Stanford-Binet scores in a 1975 review of the history of intelligence testing.[13]


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. Recent 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.[7] But 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.[14] Rushton have shown that the gains in IQ over time (the Lynn-Flynn effect) are unrelated to g.[15][16] Researchers have shown 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.[17][18][19]

Proposed explanations[edit]

Attempted explanations have included improved nutrition, a trend toward smaller families, better education, greater environmental complexity, and heterosis (the occurrence of offspring with more pronounced phenotypical traits from mixing the genes of its parents).[20] Another proposition is the gradual spread of test-taking skills.[7] The Flynn effect has been too rapid for genetic selection to be the cause.[21]

Schooling and test familiarity[edit]



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 others related to schooling is that in the US, the groups with greater test familiarity show smaller IQ increases.[7]



Generally more stimulating environment[edit]





Improved nutrition is another possible 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 by an increase in the average size of the brain.[7][26] This argument had been thought to suffer the difficulty that groups who tend to be of smaller overall body size (e.g. women, or people of Asian ancestry) do not have lower average IQs.[9] Richard Lynn, however, claims that while people of East Asian origin may often have smaller bodies, they tend to have larger brains and higher IQs than average whites.[27]



A century ago, nutritional deficiencies may have limited body and organ functionality, including skull volume. The first two years of life is a critical time for nutrition. The consequences of malnutrition can be irreversible and may include poor cognitive development, educability, and future economic productivity.[29] On the other hand, Flynn has pointed to 20-point gains on Dutch military (Raven's type) IQ tests between 1952, 1962, 1972, and 1982. He observes that the Dutch 18-year-olds of 1962 had a major nutritional handicap. They were either in the womb, or were recently born, during the great Dutch famine of 1944 – when German troops monopolized food and 18,000 people died of starvation.[30] Yet, concludes Flynn, "they do not show up even as a blip in the pattern of Dutch IQ gains. It is as if the famine had never occurred."[2][31] It appears that the effects of diet are gradual, taking effect over decades (affecting mother as well as child) rather than a few months[citation needed].

In support of the nutritional hypothesis, it is known that, in the United States, the average height before 1900 was about 10 cm (∼4 inches) shorter than it is today.[32] Possibly related to the Flynn effect is a similar change of skull size and shape during the last 150 years. Though the idea that brain size is unrelated to race and intelligence was popularized in the 1980s, studies continue to show significant correlations.[27][33] (Note, however, that size isn't everything—or maybe anything significant at all. For example, the overall size and asymmetrical shape of Albert Einstein's brain were normal; whereas the prefrontal, somatosensory, primary motor, parietal, temporal and occipital cortices were extraordinary.)[34] A Norwegian study found that height gains were strongly correlated with intelligence gains until the cessation of height gains in military conscript cohorts towards the end of the 1980s.[35] Both height and skull size increases probably result from a combination of phenotypic plasticity and genetic selection over this period.[36] With only five or six human generations in 150 years, time for natural selection has been very limited, suggesting that increased skeletal size resulting from changes in population phenotypes is more likely than recent genetic evolution.



Daley et al. (2003) found a significant Flynn effect among children in rural Kenya, and concluded that nutrition was one of the hypothesized explanations that best explained their results (the others were parental literacy and family structure).[39]

Infectious diseases[edit]





Heterosis, or hybrid vigor associated with historical reductions of the levels of inbreeding, has been proposed by Michael Mingroni as an alternative explanation of the Flynn effect. However, James Flynn has pointed out that even if everyone mated with a sibling in 1900, subsequent increases in heterosis would not be a sufficient explanation of the observed IQ gains.[44]

Possible end of progression[edit]





Lynn and Harvey have argued that the causes of the above are difficult to interpret since these countries have had significant recent immigration from countries with lower average national IQs.[citation needed] Nevertheless, they expect that similar patterns will occur, or have occurred, first in other developed nations and then in the developing world as there is a limit to how much environmental factors can improve intelligence. Furthermore, during the last century there is a negative correlation between fertility and intelligence although there is not yet any conclusive evidence of the association between the two. They estimate that there has been a dysgenic decline in the world's genotypic IQ (masked by the Flynn effect for the phenotype) of 0.86 IQ points per decade for the years 1950–2000.

IQ group differences[edit]



There is a controversy as to whether the US racial gap in IQ scores is diminishing. If that is the case then this may or may not be related to the Flynn effect. Flynn has commented that he never claimed that the Flynn effect has the same causes as the black-white gap, but that it shows that environmental factors can create IQ differences of a magnitude similar to the gap.[50] Research that has examined whether g factor and IQ gains from the Flynn effect are related have found there is a negative correlation between the two, which may indicate that group differences and the Flynn effect are possibly due to differing causes [51]


See also[edit]


  1. ^ a b Raven John (2000). "The Raven's Progressive Matrices: Change and Stability over Culture and Time" (PDF). Cognitive Psychology 41: 1–48. doi:10.1006/cogp.1999.0735. 
  6. ^ Fletcher, Richard B.; Hattie, John (11 March 2011). Intelligence and Intelligence Testing. Taylor & Francis. p. 26. ISBN 978-1-136-82321-3. Retrieved 31 August 2013. Lay summary (15 September 2013). Indeed, this effect, now called the 'Flynn effect', is well established. Nations, almost without exception, have shown gains of about 20 IQ points per generation (30 years). These gains are highest for IQ tests that are most related to reasoning and the capacity to figure out novel problems (this is often called 'fluid intelligence', see Chapter 5); and least related to knowledge, which arises from better educational opportunity, a history of persistence and good motivation for learning (this is often called 'crystallised intelligence', see Chapter 5).  Freeman, Joan (2010). Gifted Lives: What Happens when Gifted Children Grow Up. London: Routledge. pp. 290–291. ISBN 978-0-415-47009-4. Lay summary (16 May 2013). A strange new phenomenon has been growing since about 1950, called the 'Flynn Effect' after Professor James Flynn of the University of Otago, New Zealand. In his book What is Intelligence ?, Flynn describes a year-on-year rise in measured intelligence, about three IQ points a decade.  Urbina, Susana (2004). Essentials of Psychological Testing. John Wiley & Sons. p. 103. ISBN 978-0-471-41978-5. Lay summary (10 October 2013). A puzzling longitudinal trend in the opposite direction, known as the 'Flynn effect', has been well documented in successive revisions of major intelligence tests (like the S-B and the Wechsler scales) that invariably involve the administration of both the old and new versions to a segment of the newer standardization sample, for comparative purposes. Data from revisions of various intelligence tests in the United States as well as in other countries—extensively analyzed by J.R. Flynn (1984, 1987)—show a pronounced, longterm upward trend in the level of performance required to obtain any given IQ score. The Flynn effect presumably reflects population gains over time in the kinds of cognitive performance that intelligence tests sample.  Wasserman, John D. (2 October 2012). "Chapter 18: Assessment of Intellectual Functioning". In Weiner, Irving B.; Graham, John R.; Naglieri, Jack A. Handbook of Psychology. Volume 10: Assessment Psychology. John Wiley & Sons. p. 486. ISBN 978-0-470-89127-8. Retrieved 25 November 2013. Both definitions also specify that the intellectual functioning criterion for a diagnosis of intellectual disability is approximately 2 SDs or more below the normative mean, but factors such as test score statistical error (standard error of measurement), test fairness, normative expectations for the population of interest, the Flynn effect, and practice effects from previous testing need to be considered before arriving at any diagnosis.  Chamorro-Premuzic, Tomas (13 June 2011). Personality and Individual Differences. Wiley. p. 221. ISBN 978-1-4051-9927-8. Retrieved 15 June 2014. Flynn effect The finding by sociologist James Flynn that there are generational increases in IQ across nations. 
  8. ^ Trahan, LH; Stuebing, KK; Fletcher, JM; Hiscock, M (September 2014). "The Flynn effect: a meta-analysis.". Psychological Bulletin 140 (5): 1332–60. doi:10.1037/a0037173. PMID 24979188. 
  10. ^ a b Colom, R.; Lluis-Font, J.M. & 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" (PDF). Intelligence 33 (1): 83–91. doi:10.1016/j.intell.2004.07.010. 
  11. ^ Dutton Edward; Lynn Richard (2013). "A negative Flynn effect in Finland, 1997–2009". Intelligence 41: 817–820. doi:10.1016/j.intell.2013.05.008. 
  12. ^ Calhoun, Daniel (1973). The Intelligence of a People. Princeton University Press. ISBN 978-0-691-04619-8. Lay summary (6 October 2013). 
  14. ^ Must O, Must A, Raudik V (2003). "The secular rise in IQs: In Estonia, the Flynn effect is not a Jensen effect" (PDF). Intelligence 31 (5): 461–471. doi:10.1016/S0160-2896(03)00013-8. 
  15. ^ 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 Differences 26 (2): 381–9. doi:10.1016/S0191-8869(98)00148-2. 
  17. ^ 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 (5): 509537. doi:10.1016/j.intell.2004.07.002. The overall conclusion of the present paper is that factorial invariance with respect to cohorts is not tenable . . . . The fact that the gains cannot be explained solely by increases at the level of the latent variables (common factors), which IQ tests purport to measure, should not sit well with explanations that appeal solely to changes at the level of the latent variables. 
  18. ^ a b Te Nijenhuis J, De Jong MJ, 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. 
  21. ^ Blair, C.; Gamson, D.; Thorne, S.; Baker, D. (2005). "Rising mean IQ: Cognitive demand of mathematics education for young children, population exposure to formal schooling, and the neurobiology of the prefrontal cortex". Intelligence 33 (1): 93–106. doi:10.1016/j.intell.2004.07.008. CiteSeerX: 
  22. ^ Plomin R.; DeFries J.C.; Craig I.W.; McGuffin P. (2003). Behavioral genetics in the postgenomic era (4th ed.). 
  25. ^ Dickens WT, Flynn JR (2002). "The IQ Paradox: Still Resolved" (PDF). Psychological Review 109 (4): 764–771. doi:10.1037/0033-295x.109.4.764. 
  29. ^ "The Lancet Series on Maternal and Child Undernutrition". 2008. 
  35. ^ a b Sundet, J.; Barlaug, D.; Torjussen, T. (2004). "The end of the Flynn effect?: A study of secular trends in mean intelligence test scores of Norwegian conscripts during half a century". Intelligence 32 (4): 349–362. doi:10.1016/j.intell.2004.06.004. 
  37. ^ Qian M; Wang D; Watkins WE; et al. (2005). "The effects of iodine on intelligence in children: a meta-analysis of studies conducted in China". Asia Pacific Journal of Clinical Nutrition 14 (1): 32–42. PMID 15734706. 
  38. ^
  39. ^ Daley, TC; Whaley, SE; Sigman, MD; Espinosa, MP; Neumann, C (May 2003). "IQ on the rise: the Flynn effect in rural Kenyan children.". Psychological Science 14 (3): 215–9. PMID 12741743. 
  42. ^ Venkataramani, Atheendar (September 18, 2010). "Early Life Exposure to Malaria and Cognition and Skills in Adulthood: Evidence from Mexico". SSRN 1679164. 
  50. ^ Flynn, J. R. (2010). "The spectacles through which I see the race and IQ debate". Intelligence 38 (4): 363–366. doi:10.1016/j.intell.2010.05.001. 
  51. ^ Nijenhuis, J.; van der Flierb, H. (2013). "Is the Flynn effect on g?: A meta-analysis". Intelligence 41: 802–807. doi:10.1016/j.intell.2013.03.001. 

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