Sex Differences In g
Past studies of a sex difference in general ability have often been confounded by improper definitions and measurements of "general ability" based on simple summation of subtest scores from a variety of batteries that differ in their group factors, by the use of unrepresentative groups selected from limited segments of the normal distribution of abilities, and by the interaction of sex differences with age-group differences in subtest performance. These conditions often yield a mean sex difference in the total score, but such results, in principle, are actually arbitrary, of limited generality, and are therefore of little scientific interest. The observed differences are typically small, inconsistent in direction across different batteries, and, in above-average samples, usually favor males.
In this chapter sex differences are specifically examined in terms of their loadings on the g factor for a number of test batteries administered to representative population samples. When the sex differences (expressed as a point-biserial correlation between sex and scores on each of a number of subtests) were included in the correlation matrix along with the various subtests and the correlation matrix was subjected to a common factor analysis, sex had negligible and inconsequential loading on the g factor, averaging about .01 over five test batteries. Applying the method of correlated vectors to these data shows that the magnitude of the sex difference on various subtests is unrelated to the tests' g loadings. Also, the male/ female variance ratio on diverse subtests (generally indicating greater male variability in scores) is unrelated to the subtests' g loadings. Although no evidence was found for sex differences in the mean level of g or in the variability of g, there is clear evidence of marked sex differences in certain group factors and in test specific