To the Editor: We appreciate the interest and careful work of Margot Albus, M.D., Ph.D., and Werner Hubmann, M.D., on sex differences in neuropsychological functioning in schizophrenia. We have previously argued, consistent with their thinking, that the size and significance of sex effects in schizophrenia are highly dependent on methodological issues such as sampling, matching, and diagnostic criteria. However, we disagree with Drs. Albus and Hubmann regarding how one’s group should be matched to examine sex differences or group differences in neuropsychological or brain abnormalities in schizophrenic and normal subjects. The key issue is separating illness effects from presumed pre-illness characteristics, reflected in whether to match for the patients’ IQ or education or both. However, controlling for IQ or education, known to account for substantial variance in other neuropsychological measures, may remove variance directly attributable to the independent variables of interest—i.e., schizophrenia or sex (1–3). This is known as the matching fallacy (3), in which participants are overmatched on a variable that is not independent of the illness per se, such as IQ or education.