Introduction
What is new?
Key findings- •
Since our prior review, there has been a substantial increase in the number of studies describing retention strategies for in-person follow-up
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We identified and classified 985 strategies across 12 themes
What this adds to what was known?- •
This updates a prior systematic review, confirming that using a larger number of strategies is associated with a higher retention rate
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We synthesize relevant strategies and themes to be considered in the design of cohort retention plans for future studies
What is the implication and what should change now?- •
Investigators should use many strategies across different themes to optimally retain research participants for in-person follow-up
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Studies explicitly comparing the efficacy of retention strategies are needed; such studies could be embedded within in-person follow-up studies
Retention of participants plays an important role in ensuring the validity of a study and is particularly challenging in longitudinal research. Studies with a high loss to follow-up or attrition are generally judged to be of lower quality because of the increased risk of selection bias, particularly if those remaining in the study differ from those who left the study, or if there is differential attrition across the study groups being compared [1], [2].
Thus, optimizing retention of participants is an important consideration in the design and conduct of studies. This systematic review updates a prior review we conducted in 2005 on strategies to retain study participants for in-person follow-up [3]. At that time, we identified no comparative studies and 21 descriptive studies of retention strategies. We abstracted and classified each of the 368 strategies in these studies to one of 12 iteratively developed themes, finding that studies reported a median (interquartile range [IQR]) of 17 (IQR, 9 to 25) strategies across a median of six (IQR, 4 to 7) themes. Furthermore, we found that studies with a retention rate above the mean of 86% reported using more strategies (21 vs. 12; P = 0.05).
We identified two systematic reviews of retention strategies completed since the publication of our review. Both reviews were limited to studies comparing different retention methods and both considered a variety of types of follow-up (eg, in-person, phone based). Booker et al. [4] identified 28 studies, including 11 randomized controlled trials (RCTs) comparing retention strategies. This review categorized strategies as incentives, reminders, or other methods and found that incentives of cash or gifts increased retention rates in population-based cohort studies. However, only three studies included in this review considered in-person follow-up. A Cochrane review identified 38 RCTs or quasi-RCTs conducted within RCTs. The authors concluded that financial incentives increased responses to questionnaires but were unable to draw conclusions about in-person follow-up as 34 of the 38 eligible studies evaluated response to questionnaires [5], [6].
Hence, our objective was to update our prior systematic review of retention strategies for in-person follow-up in health care studies.