A clinimetric analysis of a BPRS-6 scale for schizophrenia severity

Abstract

A restricted Brief Psychiatric Rating Scale (BPRS-6) with the six schizophrenia specific items from the Positive and Negative Syndrome Scale (PANSS) has been investigated. These six items from the PANSS have recently been found to have both clinical validity and 'unidimensionality' in measuring the severity of schizophrenic states. The primary objective of this study was to evaluate the clinical validity of the BPRS-6. The secondary objective was to evaluate the 'unidimensionality' of the BPRS-6 by an 'item response theory' model. The BPRS-6 was scored independently by two psychiatrists and two psychologists while viewing six open-ended videotaped interviews in patients with a DSM-III diagnosis of schizophrenia. The interviews were conducted by Heinz E. Lehmann, an experienced psychiatrist. They were focused on the psychopathology that contributed most to the 'severity' of the patient's clinical state. The BPRS-6 with three positive symptoms (delusions, conceptual disorganisation, hallucinations) and three negative symptoms (blunted affect, emotional withdrawal, poverty of speech) was found to be clinically valid and captured the variables that contribute most to the severity of schizophrenia. The BPRS-6 was also found to have acceptable 'unidimensionality' (coefficient of homogeneity 0.45) and inter-rater reliability (inter-class-coefficient 0.81). The BPRS-6 was found to capture the information that translates into the severity of schizophrenia. It has also acceptable psychometric validity.