An empirical approach to determining criteria for abnormality in test batteries with multiple measures

Investigators and clinicians are sometimes confronted with the task of determining whether a pattern of scores on a variety of measures reflects impairment. As the number of measures increases, so does the probability that scores on some of the measures will be in the abnormal range. A simple method for setting an overall criterion for abnormality when using multiple measures is presented, and an approach for setting criteria when some of the measures are correlated is suggested. The approach is applied to a study of the neuropsychological manifestations of HIV-1 infection, and the model is found to agree with observed results.