DIAGNOSTIC classification of psychiatric patients must be based primarily on description of clinical syndromes, since definite etiological bases and the relevance of much historical data are still undetermined. Psychiatric rating scales can be conceived as mechanisms for describing, in form amenable to further quantitative evaluation, the symptoms and signs upon which psychiatric diagnoses have traditionally been based. During the last decade several rating scales have been widely used in psychiatric research, primarily to increase objectivity in evaluating the therapeutic efficacy of drug treatments.1-4The consequent availability of large collections of symptom and behavior ratings has made it possible to derive empirically a structural model representing major dimensions of clinical phenomena presented by hospitalized psychiatric patients. The Brief Psychiatric Rating Scale (BPRS) was developed to provide quantitative representation of important symptoms and signs on unitary 7-point scales.4Although the