Strategies to improve recruitment to randomised controlled trials

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Abstract
Recruiting participants to trials can be extremely difficult. Identifying strategies that improve trial recruitment would benefit both trialists and health research. To quantify the effects of strategies to improve recruitment of participants to randomised controlled trials. We searched the Cochrane Methodology Review Group Specialised Register (CMR) 2010, Issue 2, part of The Cochrane Library (online) www.thecochranelibrary.com (searched 16 April 2010); MEDLINE, Ovid (1950 to March Week 5 2010) (searched 14 April 2010); EMBASE, Ovid (1980 to 2010 Week 14) (searched 14 April 2010); ERIC, CSA (1966 to 14 April 2010); Science Citation Index Expanded, ISI Web of Science (1975 to 14 April 2010); Social Sciences Citation Index, ISI Web of Science (1975 to 14 April 2010); National Research Register (online) (Issue 3 2007) (searched 3 September 2007); C2-SPECTR (searched 9 April 2008) and PubMed 'Related citations' (searched 4 June 2010) Randomised and quasi-randomised controlled trials of methods to increase recruitment to randomised controlled trials. This includes non-healthcare studies and studies recruiting to hypothetical trials. We excluded studies aiming to increase response rates to questionnaires or trial retention, or which evaluated incentives and disincentives for clinicians to recruit patients. We extracted data on: the method evaluated; country in which the study was carried out; nature of the population; nature of the study setting; nature of the study to be recruited into; randomisation or quasi-randomisation method; and numbers and proportions in each intervention group. We used a risk or odds ratio and their 95% confidence interval (CI) to describe the effect in individual trials. We assessed heterogeneity between trial results. We identified 45 eligible trials (18 new to this update) with more than 41,239 participants. There were 40 studies involving interventions aimed directly at trial participants, while five evaluated interventions aimed at people recruiting participants. All studies were in health care. Some interventions were effective in increasing recruitment: telephone reminders to non-respondents (odds ratio (OR) 1.95, 95% CI 1.04 to 3.66; two trials, 1058 participants), use of opt-out, rather than opt-in, procedures for contacting potential trial participants (RR 1.39, 95% CI 1.06 to 1.84; one study, 152 participants) and open designs where participants know which treatment they are receiving in the trial (RR 1.22, 95% CI 1.09 to 1.36; two studies, 4833 participants). However, some of these strategies have disadvantages, which may limit their widespread use. For example, opt-out procedures are controversial and open designs are by definition unblinded. The effects of many other recruitment strategies are unclear; examples include the use of video to provide trial information to potential participants and modifying the training of recruiters. Many studies looked at recruitment to hypothetical trials and it is unclear how applicable these results are to real trials. There are promising strategies for increasing recruitment to trials: telephone reminders; requiring potential participants to opt-out of being contacted by the trial team regarding taking part in a trial, rather than them having to opt-in, and open designs. Some strategies (e.g. open trial designs) need to be considered carefully before use because they also have disadvantages. For example, opt-out procedures are controversial and open designs are by definition unblinded.