1) that the Mexico results conform to estimates from the most male-biased samples, which provide substantial underestimates of the sex difference in IQ. In the presence of strong moderators, many of the studies in the sample provide biased estimates of the sex difference in IQ score. We carried out a number of tests for moderator variables (factors that cause under- or overestimates of the sex difference) and found strong evidence for two: these were the type of test and the tendency of some universities selectively to recruit either brighter men or brighter women. This misses a central point of meta-analysis. Therefore, the fact that 21 out of 22 student samples showed a male advantage suggests the phenomenon is robust.īlinkhorn criticizes us for not adopting the principle of weighting results by sample size, and for excluding the very large study from Mexico 9. Furthermore, the idea that a null sex difference is unpublishable is belied by the huge number of books and articles, including Blinkhorn's, that claim exactly that.
Such a bias cannot be operating in this instance because, as Blinkhorn himself notes, almost none of the published literature on the Progressive Matrices has focused on sex differences. There is further evidence for a mean male advantage of 4–6 IQ points in four independent adult samples 5, 6, 7 ( n = 11,896) Jackson and Rushton 8, in a huge standardization sample ( n = 102,515) that is much bigger than the Mexico study 9, also reported a male advantage of 3.6 IQ points among 17-year-olds, which is somewhat greater than our estimates 3, 4 for this age group.Īt two points in his critique 1, Blinkhorn addresses the ‘file drawer’ problem, in which non-significant results fail to get published. This reveals no sex difference in general cognitive ability up to the age of 14 and a significant sex difference at 15, which then increases to its adult value of 5 IQ points in favour of males.
The strongest evidence for our position consists of a meta-analysis 3 derived from 57 general-population samples, many of which are normative or carefully constructed representative samples, with a total of 80,928 participants.
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