Bell Curve

Appendix 5Supplemental Material forChapter 13Three issues raised in Chapter 13 are elaborated here: a more detaileddiscussion of cultural bias, more evidence for the narrowing of the blackwhitedifference in cognitive ability, and the broader argument for racialdifferences advanced by Philippe Rushton.MORE ON TEST BIASIn Chapter 13, we reported that the scientific evidence demonstratesoverwhelmingly that standardized tests of cognitive ability are not bi.ased against blacks. Here, we elaborate on the reasoning and evidencethat lead to that conclusion.More on External Evidence of Bias: Predictive ValidityEveryday commentary on test bias usually starts with the observation thatmembers of various ethnic (or socioeconomic) groups have different averagescores and leaps to the assumption that a group difference is primafacie evidence of bias. But a moment's thought should convince anyonethat this is not necessarily so. A group difference is, in and of itself, evidenceof test bias only if we have some reason for assuming that an unbiasedtest would find no average difference between the groups. Whatmight such a reason be? We cast the answer in terms of whites and blacks,since that is the context for most charges of test bias. Inasmuch as the contextalso usually involves a criticism of the use of the test in selection ofpersons for school or job, the most pertinent reason for assuming equalityin the absence of test bias would be that we have other data showing thata randomly selected black and white with the same test score have differentoutcomes. This is what the text refers to as external evidence of bias.