Objectives: The aim of this study was to test a motivational interpretation of placebo responding using two different types of placebo therapy, one using flower essences and the other a nonspecific psychological therapy. The motivational concordance interpretation is that therapeutic rituals that are consistent with self-defining or self-actualizing goals have a nonspecific therapeutic benefit independently of expectancy.
Methods: Study 1 was a replication of an earlier flower essence outcome study but with additional outcome and predictor variables: 167 people completed questionnaires in return for free flower essence treatment. Predictor variables consisted of two measures of spirituality, optimism, expectancy, and attitudes and beliefs to complementary medicine. Outcome was assessed after 3 weeks. In Study 2, 90 people took part in "gratitude therapy" for improved sleep quality over one night in return for questionnaire completion (trait gratitude, spirituality, and expectancy).
Results: Study 1 confirmed previous research: Trait spirituality predicted perceived improvement. This improvement was independent of optimism (P<.001), cannot be explained by acquiescence or social desirability, and was independent of a highly conservative test of expectancy (P=.02). In Study 2, trait gratitude predicted perceived sleep improvement independently of expectancy (P=.01): Spirituality did not correlate with improvement.
Conclusions: These data suggest that in addition to expectations, degree of engagement in a positive, therapeutic ritual determines the extent of the placebo response. The placebo response depends in part on the interaction (i.e., the degree of concordance) between the type of therapy and the participant's personality: Dispositional predictors vary with the type of placebo therapy.