Study design affects participant expectations: a survey.

INTRODUCTION: Evidence suggests that clinical trial participants have higher expectations of improvement when they know they are receiving active treatment versus when they are aware they may receive placebo, but this has not been directly tested. The goal of this survey was to determine whether respondents report higher expectations of improvement in comparator versus placebo-controlled clinical trials.
METHOD: A questionnaire describing 2 hypothetical clinical trials was distributed to undergraduates in an introductory psychology course. The questionnaire describes 1 trial in which medication is compared with placebo and another in which the same medication is compared with another medication. Respondents rated their expectations of improvement should they participate in each trial without knowing their specific treatment assignment. Questions measured the magnitude and the likelihood of expected improvement on a 9-point Likert scale.
RESULTS: Thirty-seven undergraduates, 69% female and mean age of 22.4 +/- 6.8 years, participated in the study. Respondents reported a significantly higher expected likelihood of improvement in a comparator trial compared with a placebo-controlled trial (7.2 +/- 2.1 vs 5.3 +/- 1.6, t(36) = -4.96, P < 0.001). Similarly, they reported a significantly higher expected magnitude of improvement in a comparator trial compared with a placebo-controlled trial (7.2 +/- 1.9 vs 4.9 +/- 1.4, t(35) = -6.74, P < 0.001). DISCUSSION: These results support the hypothesis that clinical trial design influences participant expectations of improvement. Study design may affect clinical outcomes and should be kept in mind when interpreting the results of antidepressant clinical trials.

RCT Entities:   Population Interventions Outcomes