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Objective: To evaluate the effect of opt-in compared with opt-out recruitment strategies on response rate and selection bias. Design: Double blind randomised controlled trial. Setting: Two general practices in England. Participants: 510 patients with angina.Intervention: Patients were randomly allocated to an opt- in(asked to actively signal willingness to participate in research)or opt-out(contacted repeatedly unless they signalled unwillingness to participate)approach for recruitment to an observational prognostic study of patients with angina. Main outcome measures: Recruitment rate and clinical characteristics of patients. Results: The recruitment rate, defined by clinic attendance, was 38%(96/252)in the opt-in arm and 50%(128/258)in the opt-out arm(P=0.014). Once an appointment had been made, non-attendance at the clinic was similar(20%opt-in arm v 17%opt-out arm; P=0.86). Patients in the opt-in arm had fewer risk factors(44%v 60%; P=0.053), less treatment for angina(69%v 82%; P=0.01), and less functional impairment(9%v 20%; P=0.023)than patients in the opt-out arm. Conclusions: The opt-in approach to participant recruitment, increasingly required by ethics committees, resulted in lower response rates and a biased sample. We propose that the opt-out approach should be the default recruitment strategy for studies with low risk to participants.
Objective: To evaluate the effect of opt-in compared with opt-out recruitment strategies on response rate and selection bias. Design: Double blind randomised controlled trial. Setting: Two general practices in England. Participants: 510 patients with angina.Intervention: Patients Which were randomly allocated to an opt- in(asked to aggressive signal willingness to participate in research) or opt-out(contacted to multiple states unless they signalled unwillingness to participate) approach for recruitment to an observational prognostic study of patients with angina. Recruitment rate and clinical characteristics of patients. Results: The recruitment rate, defined by clinic attendance, was 38%(96/252)in the opt-in arm and 50%(128/258)in the opt-out arm(P= 0.014). Once an appointment had been made, non-attendance at the clinic was similar (20%opt-in arm v 17%opt-out arm; P=0.86). Patients in the opt-in arm had fewer risk factors( 44%v 60%; P=0.053), less treatment for angina(69%v 82%; P=0 .01), and less functional impairment(9%v 20%; P=0.023)than patients in the opt-out arm. Conclusions: The opt-in approach to participant recruitment, increasingly required by ethics committees, resulted in lower response rates And a biased sample. We propose that the opt-out approach should be the default recruitment strategy for studies with low risk to participants.