Systematic review identifies number of strategies important for retaining study participants

Objective: Loss to follow-up threatens internal and external validity yet little research has examined ways to limit participant attrition. We conducted it systematic review of studies with a primary focus on strategies to retain participants in health care research. Study Design and Settings: We completed searches of PubMed, CINAHL, CENTRAL, Cochrane Methodology Register, and EMBASE (August 2005). We also examined reference lists of eligible articles and relevant reviews. A data-driven thematic analysis of the retention strategies identified common themes. Results: We retrieved 3,068 citations, 21 studies were eligible for inclusion. We abstracted 368 strategies and from these identified 12 themes. The studies reported a median of 17 strategies across a median of six themes. The most commonly reported strategies were systematic methods of participant contact and scheduling. Studies with retention rates lower than the mean rate (86%) reported fewer strategies. There was no difference in the number of different themes used. Conclusion: Available evidence suggests that investigators should consider using a number of retention strategies across several themes to maximize the retention of participants. Further research, including explicit evaluation of the effectiveness of different strategies, is needed. (C) 2007 Elsevier Inc. All rights reserved.