The Totality of Available Evidence Shows the Race IQ Gap Still Remains

Abstract

In a previous study (Rushton & Jensen, 2005), we examined 10 categories of technical research and concluded that the mean Black-White IQ difference in the United States is about 80% heritable. We reviewed evidence that (a) the distribution of IQ scores around the world shows averages of 106 for East Asians, 100 for Whites, 85 for U.S. Blacks, and 70 for sub-Saharan Africans; (b) race differences are most pronounced on the more g-loaded subtests (g being the general factor of mental ability); (c) race differences are most pronounced on the subtests whose scores show the most heritability; and (d) racial differences in brain size parallel the IQ differences. We also reviewed corroborating studies of (e) racial admixture, (f) trans-racial adoption, (g) regression to different racial means, (h) 60 related life-history traits, (i) human origins, and (j) the inadequacy of environmental explanations of the racial IQ difference. (In Africa, the 30-point difference is likely only 50% heritable because environmental factors such as malnutrition and disease have so much more impact than they do elsewhere in the world; Lynn, 2006.) Dickens and Flynn (2006, this issue) challenge our hypothesis. They claim that ‘‘no one can really trace the Black-White IQ gap in the United States back to its origins’’ (p. 913) and that in the United States, Blacks have gained ‘‘4 to 7 IQ points on non-Hispanic Whites between 1972 and 2002’’ (p. 913). But to maintain that ‘‘no one can really trace the . . . gap back to its origins,’’ Dickens and Flynn had to sidestep our citation of Shuey’s (1966) review of the literature, which shows that BlackWhite IQ differences in the United States have remained at 15 to 18 points, or 1.1 standard deviations, for nearly a century. For example, she found 23,596 Black draftees in World War I (1917) had an IQ of 83 (vs. 100 for Whites), with a Black overlap of the White mean of 13%. For recent data, we cited the meta-analysis by Roth, Bevier, Bobko, Switzer, and Tyler (2001), which also shows a mean difference of 1.1 standard deviations (range of 0.38 to 1.46 standard deviations, depending on the test’s g loading), based on 6,246,729 individuals from military, corporate, and higher-education samples. Roth et al. found any narrowing of the gap was ‘‘either small, potentially a function of sampling error . . . or nonexistent for highly g loaded instruments’’ (p. 323, italics added). To claim a 4to 7-point gain for Blacks, Dickens and Flynn chose three independent tests showing medium gains (the Wechsler, Stanford-Binet, and Armed Forces Qualification tests) and relegated to their Appendix B four or more tests showing lesser gains. They excluded the Wonderlic Personnel Test, which they acknowledge showed a gain of only 2.4 points for Blacks between 1970 and 2001. (Dickens and Flynn suggest that more ‘‘high quality’’ Whites than Blacks had taken the test.) They excluded the Kaufman Assessment Battery for Children (K-ABC), which Murray (2005) described as showing a loss of 1 IQ point for Blacks between 1983 and 2004. (Dickens and Flynn say the data contained an inflated standard deviation.) They excluded the very g-loaded Woodcock-Johnson test, which Murray (2005; whom they cite) described as showing the conventional gap of 1.05 standard deviations for the third (2001) standardization sample. (Dickens and Flynn say the Blacks were an unrepresentative ‘‘subsubsample.’’) They also excluded the Differential Ability Scale, which in Lynn’s (1996) analysis (which they cite) showed a maximum gain of 1.83 IQ points for Blacks between 1972 and 1986. (Dickens and Flynn say the sample lacked ‘‘quality.’’) To be compelling, however, researchers must take the totality of available evidence into account (Gottfredson, 2005). Even the tests Dickens and Flynn did analyze do not support their conclusion. The alleged gain of 4 to 7 points is from a ‘‘projected’’ trend line based on a small IQ rise per year multiplied by more years than are in the data using unclear procedures (see the additional appendix in the Web site they refer to). Simple arithmetic applied to the data in their Table A1 shows a mean gain for Blacks of only 3.44 IQ points, from 86.44 to 89.88 Address correspondence to J. Philippe Rushton, Department of Psychology, University of Western Ontario, London, Ontario N6A 5C2, Canada, e-mail: rushton@uwo.ca. PSYCHOLOGICAL SCIENCE