Date of Award


Publication Type

Doctoral Thesis

Degree Name




First Advisor

Sirois, Fuschia (Psychology)


Psychology, Psychobiology.




The placebo effect has become recognized as an excellent example of mind-body interaction and as a mechanism of therapeutic action in its own right. Theoretical and empirical work has shown that expectations of treatment are important mediators of placebo effects, as well as treatment outcomes in diverse areas of health care. Modern theorists agree that situational and individual factors both contribute to the formation of treatment expectancies; however, only the former has received adequate study. The current research was designed to identify psychosocial variables associated with positive treatment expectations, using irritable bowel syndrome (IBS) as an illness model. People with IBS (n = 289) were recruited online to read hypothetical vignettes about treatments for IBS and to rate their expectations to benefit from treatment on a continuous scale. Participants completed a questionnaire battery measuring various individual difference factors, health belief variables and context-specific psychosocial variables, all identified from the literature as potentially relevant correlates of levels of expectation. Correlation and regression analyses revealed that several of these variables were positively associated with ratings of expected treatment benefit, in particular, perceived somatic focus of treatment, beliefs of personal control over symptoms, levels of optimism and self-focused attention. Weaker relationships were identified for acute health status, coping self-efficacy, catastrophizing and patient-provider relationship; whereas no relationships were found for trait anxiety or motivational factors. Among those with past experience with similar treatments, previous treatment satisfaction was a strong predictor of current expectations. Supplemental analyses revealed that among a sub-sample having previous treatment experience, along with higher levels of self-focused attention, significant relationships between treatment expectancies and independent psychosocial variables were more numerous and more robust. Results are discussed in light of contributions to theory, directions for future research as well as potential clinical applications.