Antecedent probability and the efficiency of psychometric signs, patterns, or cutting scores.

In clinical practice, psychologists frequently participate in the making of vital decisions concerning the classification, treatment, prognosis, and disposition of individuals. In their attempts to increase the number of correct classifications and predictions, psychologists have developed and applied many psychometric devices, such as patterns of test responses as well as cutting scores for scales, indices, and sign lists. Since diagnostic and prognostic statements can often be made with a high degree of accuracy purely on the basis of actuarial or experience tables (referred to hereinafter as base rates), a psychometric device, to be efficient, must make possible a greater number of correct decisions than could be made in terms of the base rates alone. The efficiency of the great majority of psychometric devices reported in the clinical psychology literature is difficult or impossible to evaluate for the following reasons: a. Base rates are virtually never reported. It is, therefore, difficult to determine whether or not a given device results in a greater number of correct decisions than would be possible solely on the basis of the rates from previous experience. When, 1 From the Neuropsychiatric Service, VA Hospital, Minneapolis, Minnesota, and the Divisions of Psychiatry and Clinical Psychology of the University of Minnesota Medical School. The senior author carried on his part of this work in connection with his appointment to the Minnesota Center for the Philosophy of Science.