Prediction of positive placebo response among chronic schizophrenic outpatients

We undertook this study to determine whether predictors of positive placebo response in chronic schizophrenic outpatients could be identified. Twelve placebo responders and 33 placebo nonresponders who participated in a parallel-group, double-blind, 12-week clinical drug trial were compared. No significant differences between the groups were found with regard to 16 anamnestic and symptom variables. To investigate further which variables at baseline predicted positive placebo response, a stepwise linear regression model was created. Of the seven variables entered into the model, only high scores in the positive domain of the Positive and Negative Syndrome Scale (delusions, unusual thought content, grandiosity, and suspiciousness/persecution) at baseline predicted significantly positive placebo response (p = .0047). Because the onset of placebo response was gradual, the authors hypothesize that placebo response in chronic schizophrenia consists mainly of two ingredients: nonspecific psychotherapeutic effect caused by the several assessments carried out during the study, and regression toward the mean.