Background: Ethical aspects of prevention trials, as they differ from therapeutic trials, have not been fully explored. This article aims to define and demonstrate the existence of "preventive misconception" (PM), a misunderstanding in which research participants in prevention trials make an "overestimate in probability or level of personal protection that is afforded by being enrolled in a trial of a preventive intervention."
Methods: A rating tool was developed to evaluate PM, using data collected between August 2000 and July 2002 as part of a nationwide study of the quality of informed consent in a trial of a shingles vaccine. During 2005-2006, two pair of raters assessed the responses of 50 participants to questions asked after the participants had given consent to participate in the shingles trial. Two pair of raters evaluated the response for the presence and type of PM. Each pair of raters adjudicated their responses and inter-rater reliability was assessed.
Results: Adjudicated pairs of raters agreed that 32% (CI: 20.7%-45.9%) of participants showed evidence of PM (kappa=0.71, CI: 0.52-0.90); that 12% (CI: 5.2%-24.2%) of participants underestimated the probability of receiving placebo (kappa=0.53, CI: 0.24-0.83); and that 24% (CI: 14.2%-37.6%) overestimated the likely personal effectiveness of the experimental intervention (kappa=0.42, CI: 0.08-0.76).
Conclusions: This study newly describes the concept of preventive misconception and empirically demonstrates its existence in trials of prevention. Study participants may overestimate the protection that they receive by being enrolled in a trial of prevention, which poses ethical challenges for research.