Background. Efficacy of patient decision aids (PtDAs) may be influenced by trial participants' identity either as patients seeking to benefit personally from involvement or as volunteers supporting the research effort. Aim. To determine if study characteristics indicative of participants' trial identity might influence PtDA efficacy. Methods. We undertook exploratory subgroup meta-analysis of the 2011 Cochrane review of PtDAs, including trials that compared PtDA with usual care for treatment decisions. We extracted data on whether participants initiated the care pathway, setting, practitioner interactions, and 6 outcome variables (knowledge, risk perception, decisional conflict, feeling informed, feeling clear about values, and participation). The main subgroup analysis categorized trials as volunteerism or patienthood on the basis of whether participants initiated the care pathway. A supplementary subgroup analysis categorized trials on the basis of whether any volunteerism factors were present (participants had not initiated the care pathway, had attended a research setting, or had a face-to-face interaction with a researcher). Results. Twenty-nine trials were included. Compared with volunteerism trials, pooled effect sizes were higher in patienthood trials (where participants initiated the care pathway) for knowledge, decisional conflict, feeling informed, feeling clear, and participation. The subgroup difference was statistically significant for knowledge only (P = 0.03). When trials were compared on the basis of whether volunteerism factors were present, knowledge was significantly greater in patienthood trials (P < 0.001), but there was otherwise no consistent pattern of differences in effects across outcomes. Conclusions. There is a tendency toward greater PtDA efficacy in trials in which participants initiate the pathway of care. Knowledge acquisition appears to be greater in trials where participants are predominantly patients rather than volunteers.
