Equipercentile linking of the Brief Psychiatric Rating Scale and the Clinical Global Impression Scale in a catchment area.

Recent analyses tried to explain the meaning of the Brief Psychiatric Rating Scale total score (BPRS) and its percentage change from baseline by equipercentile linking with the Clinical Global Impression Scale (CGI). A major limitation was that they were conducted in clinical trial populations limiting generalisability to 'real-world' patients. We therefore replicated the findings in a large sample covering patients admitted to a state hospital with a catchment area. BPRS and CGI ratings at admission (n=1772) and at discharge from all patients with schizophrenic disorders (ICD-10 F20.0-F20.9) admitted between 2005 and 2008 were compared using equipercentile linking. Being considered "mildly ill" according to the CGI severity score approximately corresponded to a BPRS total score of 25, "moderately ill" to a BPRS of 33-35, "markedly ill" to a BPRS of 50 and severely ill to a BPRS of 70. To be "minimally improved" according to the CGI change score was associated with a mean BPRS reduction of 13%; and "much improved" with 50% BPRS reduction. The linking functions were not identical, but overall comparable to those in previous randomised trial samples. The suggestion that a 50% BPRS reduction from baseline is a clinically meaningful definition of response in acutely ill patients was reinforced.