Eliciting harms data from trial participants: how perceptions of illness and treatment mediate recognition of relevant information to report

Background There is no consensus on the ideal methodology for eliciting participant-reported harms, but question methods influence the extent and nature of data detected. This gives potential for measurement error and undermines meta-analyses of adverse effects. We undertook to identify barriers to accurate and complete reporting of harms data, by qualitatively exploring participants’ experiences of illness and treatment, and reporting behaviours; and compared the number and nature of data detected by three enquiry methods.