Sacked, Borne man, and Connelly recently discussed several criticisms that are often raised against the use of cognitive tests in selection. One criticism concerns the issue of measurement bias in cognitive ability tests with respect to specific groups in society. Sacked et AL. (2008) stated that "absent additional information, one cannot determine whether mean differences [in test scores] reflect true differences in the developed ability being measured or bias in the measurement of that ability" (p. 222). Their discussion of measurement bias appears to suggest that measurement bias in tests can be accurately detected through the study of differential prediction of criteria across groups. In this comment, we argue that this assertion is incorrect. In fact, it has been known for more than a decade that tests of differential regression are not generally diagnostic of measurement bias (Millsap, 1997, 1998, 2008). (Contains 1 figure.)