BMJ  2005;331 (22 October), doi:10.1136/bmj.331.7522.0-b

Ethics may lead to bias: recruitment

Ethical committees increasingly require participant recruitment to be done by the "opt-in" approach (with potential participants asked to actively signal willingness to participate in research). But this seems to result in lower response rates and a biased sample compared with the "opt-out" approach (which assumes willingness to participate unless potential participants actively signal their unwillingness). Junghans and colleagues (p 940) randomised 510 patients with angina to either method when recruiting for an observational study. Compared with those in the opt-out arm, patients in the opt-in arm had significantly fewer risk factors (44% v 60%), less treatment for angina (69% v 82%), and less functional impairment (9% v 20%).

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Relevant Article

Recruiting patients to medical research: double blind randomised trial of "opt-in" versus "opt-out" strategies

Cornelia Junghans, Gene Feder, Harry Hemingway, Adam Timmis, and Melvyn Jones
BMJ 2005 331: 940. [Abstract] [Full Text] [PDF]