The publication of The Bell Curve (Herrnstein & Murray, 1994) incited a heated public debate over the concept of intelligence and the meaning of intelligence test score. In November, 1984, the Board of Scientific Affairs of the American Psychological Association established a Task Force to write an review of the research findings in the fields of intelligence and intelligence testing; the following is a brief summary of their findings in regard to intelligence tests as predictors (Neisser et al, 1996).

Intelligence tests scores remain fairly stable as a child develops. Jones and Bayley(1941) found a correlation of r=0.77 between scores at ages 6 and 18, and r=0.89 between scores at ages 12 and 18. However, individuals' IQ scores did change; the average change between ages 12 and 17 was 7.1 points. Conventional infant intelligence tests scores have shown low predictive validity in children under 6. However, habituation-based measures of infant intelligence have shown better predictive validity (a recent meta-analysis found an average r=0.36; McCall & Garriger, 1993).

Although they sample a rather limited base of questions, intelligence tests are fairly good predictors of many outcomes. The correlation between IQ test scores and grades in school is about 0.50. However, it should be noted that, although this correlation is high, it means that 75% of the variance in grades is attributable to factors other than the "intelligence" that is measured by IQ tests. Factors such as motivation, encouragement, and peer pressure are also important factors in a child's school achievement. Intelligence tests also show correlations between r=0.30 and r=0.50 with measures of job performance. Again, these correlations only explain between 9 and 25% of the variance in job performance. Finally, IQ test scores show low negative correlations with negative social outcomes such as juvenile offenses.

Overall, intelligence tests scores at younger ages are fairly good predictors of scores at later ages; however, people's IQ scores can and do change over time. And although IQ scores are highly correlated with school and job performance, "intelligence" is not the only important factor influencing these outcomes.

References
Herrnstein, R.J., & Murray, C. (1994). The bell curve: Intelligence and class structure in American life. New York: Free Press.

Jones, H.E., & Bayley, N. (1941). The Berkeley Growth Study. Child Development, 12, 167-173.

McCall, R.B., & Garriger, M.S. (1993). A meta-analysis of infant habituation and recognition memory performance as predictors of later IQ. Child Development, 64, 57- 79.

Neisser, U., Boodoo, G., Bouchard, T.J., Jr., Boykin, A.W., Brody, N., Ceci, S.J., Halpern, D.F., Loehlin, J.C., Perloff, R., Sternberg, R.J., & Urbina, S. (1996). Intelligence: Knowns and unknowns. American Psychologist, 1996, 51, 77-101.

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