Relationship between the Brief Psychiatric Rating Scale and the Scale for the Assessment of Negative Symptoms: a study of their correlation and redundancy.

Because overlapping psychometric scales are used frequently in psychiatric research, examination of the relationship between scales has become increasingly important. The concept of relationship is the focus of this article. By way of illustration, the Brief Psychiatric Rating Scale (BPRS) and the Scale for the Assessment of Negative Symptoms (SANS) were compared for correlation and redundancy. Since these scales are frequently represented by derived summary variables (e.g., factors, total scores), it is also important to assess the effect of such representation on measures of relationship. The SANS and the BPRS were found to be highly intercorrelated. Nevertheless, the individual items and the subscale scores of the SANS contain information independent from the BPRS: the best BPRS predictor variates can explain only approximately half of the total variance of the SANS. When the SANS, however, is represented by a single variable (composite score), it becomes highly redundant with the anergia factor of the BPRS.