Skip to main content

What is intelligence? Beyond the Flynn effect


Around their 18th birthday, basically all Dutch males born between 1934 and 1964 unknowingly took part in a study of the malleability of intelligence. When these young men appeared before the Dutch military draft board, they took a non-verbal IQ test based on Raven’s (1960) Progressive Matrices. With a little help from Piet Vroon, James Flynn (1987) discovered that those born in 1934 (cohort of 1952) scored on average 20 IQ points lower on the test than those born in 1964 (cohort of 1982). This suggested that in only 30 years, the Dutch male population had shown an increase of more than one standard deviation in average IQ. Flynn (1987) also documented this gain in average IQ in 13 other countries over the course of the 20th century and the effect is now commonly known as the Flynn effect. The Flynn effect raises many questions: How can IQ be substantially heritable, yet show such strong gains that appear to be due to environmental factors? Were Dutch males in 1982 so much smarter than Dutch males in 1952?

This is a preview of subscription content, access via your institution.


  1. Dickens, W.T. (2007). What is g? Paper presented at the Schelling Symposium, University of Maryland, College Park, MD.

  2. Dickens, W.T. & Flynn, J.R. (2001). Heritability estimates versus large environmental effects: The IQ paradox resolved. Psychological Review, 108, 346-369.

    Article  CAS  PubMed  Google Scholar 

  3. Flynn, J.R. (1987). Massive IQ gains in 14 nations: What IQ tests really measure. Psychological Bulletin, 101, 171-191.

    Article  Google Scholar 

  4. Flynn, J.R. (2007). What is intelligence? Beyond the Flynn Effect. Cambridge, UK: Cambridge University Press.

    Google Scholar 

  5. Greenfield, P.M. (1998). The cultural evolution of IQ. In U. Neisser (Ed.), The rising curve: Long-term gains in IQ and related measures. Washington, DC: American Psychological Association.

    Google Scholar 

  6. Okagaki, L. & Frensch, P.A. (1994). Effects of video game playing on measures of spatial performance: Gender effects in late adolescence. Journal of Applied Developmental Psychology, 15, 33-58.

    Article  Google Scholar 

  7. Raven, J.C. (1960). Guide to the Standard Progressive Matrices. London: H.K. Lewis & Co. Ltd.

    Google Scholar 

  8. Spearman, C. (1904). General intelligence, objectively determined and measured. American Journal of Psychology, 15, 201-292.

    Article  Google Scholar 

  9. Stinissen, J., Willems, P.J., Coetsier, P., & Hulsman, W.L.L. (1970). Handleiding bij de Nederlandstalige bewerking van de Wechsler Adult Intelligence Scale (WAIS). [Dutch WAIS Manual]. Lisse, the Netherlands: Swets and Zeitlinger.

    Google Scholar 

  10. van der Maas, H.L.J., Dolan, C.V., Grasman, R.P.P.P., Wicherts, J.M., Huizenga, H.M. & Raijmakers, M.E.J. (2006). A dynamical model of general intelligence: the positive manifold of intelligence by mutualism. Psychological Review, 113, 842-861.

    Article  PubMed  Google Scholar 

  11. Wicherts, J.M., Dolan, C.V., Hessen, D.J., Oosterveld, P., van Baal, G.C.M., Boomsma, D.I., et al. (2004). Are intelligence tests measurement invariant over time? Investigating the nature of the Flynn effect. Intelligence, 32, 509-537.

    Article  Google Scholar 

Download references

Author information



Corresponding author

Correspondence to Jelte M. Wicherts.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Wicherts, J.M. What is intelligence? Beyond the Flynn effect. NEJP 64, 41–43 (2008).

Download citation


  • Differential Item Functioning
  • General Intelligence
  • Verbal Intelligence
  • Differential Item Functioning Analysis
  • Comprehension Subtest