Is there a linear relationship between the Brief Psychiatric Rating Scale and the Clinical Global Impression-Schizophrenia scale? A retrospective analysis

Abstract

BackgroundAlthough the Brief Psychiatric Rating Scale (BPRS) is widely used for evaluating patients with schizophrenia, it has limited value in estimating the clinical weight of individual symptoms. The aim of this study was 4-fold: 1) to investigate the relationship of the BPRS to the Clinical Global Impression-Schizophrenia Scale (CGI-SCH), 2) to express this relationship in mathematical form, 3) to seek significant symptoms, and 4) to consider a possible modified BPRS subscale.MethodsWe evaluated 150 schizophrenia patients using the BPRS and the CGI-SCH, then examined the scatter plot distribution of the two scales and expressed it in a mathematical equation. Next, backward stepwise regression was performed to select BPRS items that were highly associated with the CGI-SCH. Multivariate regression was conducted to allocate marks to individual items, proportional to their respective magnitude. We assessed the influence of modifications to the BPRS in terms of Pearson's r correlation coefficient and r-squared to evaluate the relationship between the two scales. Utilizing symptom weighting, we assumed a possible BPRS subscale.ResultsBy plotting the scores for the two scales, a logarithmic curve was obtained. By performing a logarithmic transformation of the BPRS total score, the curve was modified to a linear distribution, described by [CGI-SCH] = 7.1497 × log10[18-item BPRS] - 6.7705 (p < 0.001). Pearson's r for the relationship between the scales was 0.7926 and r-squared was 0.7560 (both p < 0.001). Applying backward stepwise regression using small sets of items, eight symptoms were positively correlated with the CGI-SCH (p < 0.005) and the subset gave Pearson's r of 0.8185 and r-squared of 0.7198. Further selection at the multivariate regression yielded Pearson's r of 0.8315 and r-squared of 0.7036. Then, modification of point allocation provided Pearson's r of 0.8339 and r-squared of 0.7036 (all these p < 0.001). A possible modified BPRS subscale, "the modified seven-item BPRS", was designed.ConclusionsLimited within our data, a logarithmic relationship was assumed between the two scales, and not only individual items of the BPRS but also their weightings were considered important for a linear relationship and improvement of the BPRS for evaluating schizophrenia.

A Modification of the Relative Weightings of Symptoms Utilizing a Logistic Function to Enhance the Linearity of the Brief Psychiatric Rating Scale: A Retrospective Analysis

“…Pearson's r coefficient for the relationship between the 18-item BPRS and the CGI-SCH was 0.8216 (p < 0.001) and r-squared (that of multivariate linear regression using all items of the BPRS) was 0.7718 (p-value of ANOVA was less than 0.001). On the scatter plot, there was a rough correlation where a curve with upper convexity was obtained and the straight-line relationship that had been thought to exist between the two scales was not apparent (this is also described in our previous report [7]). Because the shape of the curve was similar to a logarithmic curve, we performed a natural logarithmic transformation of the 18-item BPRS total score.…”

“…From this result, we presumed that there was a possibility that an increase in the logarithm of the total score for all symptoms might be roughly proportional to the global increase in symptom severity observed clinically in schizophrenic patients that was mentioned in our previous report [7]. Also in this report, we presumed that the logarithmic relationship between the single score scale, the CGI-SCH, and the plural score scale, the BPRS, might be an important tool in our determination of the severity of illness (e.g., there might be a possibility that a clinician's impression of the severity of a certain disease is approximately proportional not to the simple sum of respective severity of symptom ratings but to the logarithm of this sum).…”

“…Another crucial reason for this choice is that, with multivariate regression analyses, we often obtain regression coefficients of independent variables that are inversely associated with the dependent variable. In our previous study, by performing multivariate regression, some symptoms of the BPRS were inversely correlated with the CGI-SCH, although the phenomenon of the higher score on some symptoms implying a less ill state was a departure from clinicians' experiences [7]. To be sure, there might be a case where independent variables are inversely correlated with a dependent variable in multivariate regression, even though the independent variables have positive correlations in their respective univariate regression analyses (utilizing each variable as the only independent variable).…”

“…We decided to investigate this divergence analytically, looking at the clinical weights of various symptoms (the relative magnitudes of symptoms in schizophrenia) and the issue of scale nonlinearity. It was discussed in our previous report that there might not be a linear relationship between the two scales (the shape of distribution between them was assumed to be a logarithmic curve) and that the degree of linearity between the BPRS and the CGI-SCH might be influenced not only by the former's selection of items but also by modification of the points allocated to each symptom [7]. However, there was a crucial weakness in this analysis as some items of the BPRS were excluded.…”

Differences in Clinical Features of Methamphetamine Users with Persistent Psychosis and Patients with Schizophrenia

“…All items were rated on a 7-point Likert scale, with higher scores indicating greater severity. Subscale scores were calculated using small sets of variables based on the 3 domains of the Positive and Negative Syndrome Scale (PANSS): positive, negative, and general psychopathological symptoms [33]. In addition, the lifetime experience of participants of various forms of delusions (e.g.…”