In his study of IQ tests scores for different populations over the past sixty years, James R. Flynn discovered that IQ scores increased from one generation to the next for all of the countries for which data existed (Flynn 1990). This interesting phenomena has been called "the Flynn Effect." Many of the questions about why this effect occurs have not yet been answered by researchers. This site attempts to explain the issues involved in a way that will better help you to understand the Flynn Effect. It also provides references for further inquiry.
Research shows that IQ gains have been mixed for different countries. In general, countries have seen generational increases between 5 and 25 points. The largest gains appear to occur on tests that measure fluid intelligence (Gf) rather than crystallized intelligence (Gc).
Tests like the Ravens, the Norwegian matrices, the Belgian Shapes test, the Jenkins test, and the Horn test are examples of tests that attempt to measure fluid intelligence. These tests try to emphasize problem solving and minimize a reliance on specific skills or familiarity with words and symbols. These tests on average have shown an increase of about 15 points or one standard deviation per generation (Flynn 1994/1987 & Deary 2001) notes that it is these types of tests (i.e., "culturally reduced") on which we would not expect to see score increases if the cause of the increases was due to educational factors.
Tests like the Wechsler-Binet and purely verbal tests measure crystallized intelligence in addition to fluid intelligence. Some questions on these tests measure problem solving abilities but others measure learned information such as vocabulary and math skills. The IQ gains for these tests have been more moderate, with an average of about 9 points per generation
Flynn, J. R. (1984). The mean IQ of Americans: Massive gains 1932 to
1978. Psychological Bulletin, 95, 29-51.
Jensen, A. R. (1989). Rising IQ without increasing g? [A review of The Milwaukee Project: Preventing mental retardation in children at risk]. Development Review, 9, 234-258.
Lynn, R. (1987). Japan: Land of the rising IQ, A reply to Flynn. Bulletin of the British Psychological Society, 40, 464-468.
Neisser, U. (Ed.). (1998). The rising curve. Washington, DC: American Psychological Association.
Raven, J. C., Court, J. H., & Raven, J. (1992). Manual for Raven's progressive matrices and vocabulary scales (section 3). Oxford: Oxford Psychologist Press.
source and more information: http://www.indiana.edu/~intell/flynneffect.shtml#intro & http://www.sciencedirect.com/science/article/pii/S0891422210001526
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