Objective: Loss to follow-up threatens internal and external validity yet little research has examined ways to limit participant attrition. We conducted a 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.