Perceptions of Credibility of Treatment and Placebo by Treated and Quasi-Control Subjects

Abstract

This study compared two methods for obtaining ratings on treatment credibility/expectancy-for-improvement. 100 students either received actual intervention for speech anxiety (“treated” subjects) or simply read procedural descriptions and rationales of two treatment methods and a placebo strategy (“written exposure” subjects). Although there were no differences in ratings of credibility initially, treated subjects' ratings were significantly higher than those given written exposure by the end of the treatment. The findings suggest that researchers assess credibility within the context of actual intervention rather than rely exclusively on “quasi-control” data. The former method may provide a stronger basis for determining whether differences in outcome between groups are attributable to active therapeutic ingredients or to clients' differential expectancies for change.