How evidence based are recruitment strategies to randomized controlled trials in primary care? Experience from seven studies

Background. Failure to recruit adequate numbers of participants represents a major barrier to the completion of randomized controlled trials in primary care and is associated with substantial opportunity costs. However, uncertainty exists regarding the relative effectiveness of different methods to promote recruitment. Objectives. The purpose of this study was to estimate the proportion of strategies used to promote patient recruitment to randomized controlled trials in primary care that are evidence based. Methods. Investigators from seven primary care-based clinical trials of dyspepsia management aiming to recruit a total of 6070 patients participated. Following a survey of trial organization, a Delphi technique was used to reach consensus on levels of evidence on the effectiveness of interventions or organizational characteristics in influencing recruitment. The main outcome measures were the proportions of interventions or organizational characteristics for influencing patient recruitment that are based upon randomized controlled trials, on convincing nonexperimental evidence or meeting neither of these criteria. Results. Out of a total of 56 interventions used across the trials, 35 (63%) were judged as evidence based. Out of a total of 29 organizational characteristics possessed by the trials, five (17%) were judged as evidence based. Across the seven dyspepsia trials, the presence of 'favourable' organizational characteristics appeared to be important contributors towards successful recruitment. Conclusions. A wide range of interventions and organizational characteristics with the potential to promote recruitment were used or possessed by seven primary care trials. Many were not evidence based. Our experience suggests that organizational characteristics could be more influential in trial recruitment than the use of specific interventions. Given the costs of primary care-based trials, researchers need more rigorous evidence to inform recruitment strategies.