BackgroundResearchers worry that patients in early-phase research experience unrealistic optimism about benefits and risks of participation. The standard measure of unrealistic optimism is the Comparative Risk/Benefit Assessment questionnaire, which asks people to estimate their chances of an outcome relative to others in similar situations. Such a comparative framework may not be a natural way for research participants to think about their chances.ObjectiveTo examine how people interpret questions measuring unrealistic optimism and how their interpretations are associated with their responses.MethodsUsing an early-phase (...) cancer trial vignette, we administered the CRBA to 297 adults from the general public. They estimated their comparative chances of risk and benefit, then provided rationales for their estimates.ResultsFor both CRBA benefit and risk questions, about 50% of respondents chose 0, and 50% chose a non-0 response. Respondents’ rationales for their estimates showed that overall only about 40%–44% gave comparative rationales, indicating that they interpreted the CRBA as intended. 68.7% of respondents who gave the ‘correct’ 0 rating gave comparative rationales, whereas only 11.6% of respondents who gave non-0 ratings did so. A similar trend was seen for chances of risk.ConclusionResearch participants may not understand comparative benefit and risk questions as intended; attributions of unrealistic optimism may require additional evidence that the respondents’ estimates are intended to be comparative. (shrink)