Review ArticleSystematic review identifies number of strategies important for retaining study participants
Introduction
Loss to follow-up of research participants threatens the internal and external validity of a study [1], [2]. The study results may be biased by differential dropout between comparison groups or by differences between those participants who drop out and those that continue to participate. Loss to follow-up may also threaten the generalizability of a study, as well as its statistical power. Despite these threats, little attention has been paid to the optimal methods of maintaining participants in a study.
Much of the existing literature on strategies to retain participants in research studies is limited to descriptions of “lessons learned.” For example, based on their experiences in studies of people aged over 65 years, Cassidy et al. suggested that personalized attention, empathy, and support from study staff resulted in higher participant completion [3]. Shumaker et al. similarly drew on their own experiences to outline approaches to promote retention including screening out those likely to not remain in the study and early identification and tracking of study participants who are poor or nonadherers [4].
Coday et al. collected lessons learned from 14 NIH-funded behavioral change trials [5]. They elicited perceived barriers to participant retention and 61 retention strategies from the project staff and investigators from these trials. The retention strategies were categorized into eight themes which study personnel then ranked based on perceived effectiveness. The strategy category of flexibility followed by incentives, benefits, and persistence were rated as most effective by the study personnel.
Davis et al. completed a review of trials between 1990 and 1999 identifying 21 studies that included a description of retention strategies and retention rates [6]. The authors provided a table listing the trials rank-ordered based on the retention rate (specifics not provided) and suggested that those studies with higher retention were those using a combination of strategies. The paper combined discussion about retention and recruitment strategies as well as about studies with mail or telephone follow-up vs. those with in-person visits.
In the existing literature, we could not identify any explicit evaluation of the effectiveness of retention strategies, such as a comparison of follow-up rates using different strategies. To help comprehensively synthesize strategies for participant retention in research studies and to evaluate areas for future methodological research in this field, we conducted a systematic review of studies which described strategies for maximizing retention for in-person follow-up.
Section snippets
Searching and study selection
We sought English-language publications reporting research that described retention strategies for in-person follow-up and included actual retention rates. We reviewed only those published reports with a primary focus on retention strategies. We included studies that provided data on retention rates, described data from a primary study, and provided information regarding strategies used to retain participants. We searched PubMed (August 11, 2005), Cumulative Index of Nursing and Allied Health
Review process
Our search identified 3,068 potentially relevant citations of which 115 were considered further at the full-text level. Of these 115, we excluded an additional 94 primarily because the article did not describe a primary study (e.g., article was a review or commentary) or because the article did not describe specific retention strategies. There were 21 articles that met our eligibility criteria. Fig. 1 summarizes the results of our search and selection processes.
Study characteristics
The 21 studies in this review
Discussion
Failure to retain study participants in a research study is an important methodological concern. Given the expense of conducting health care research, the limited financial resources to support such studies and the risks patients potentially incur from participation, efforts to reduce bias from loss to follow-up are an important research priority. Large overall loss to follow-up or differential loss to follow-up threatens the internal and external validity of studies and limits the ability to
Acknowledgments
We thank Rameswari Radhakrishnan for development of the relational database and data entry.
This research is supported by National Institutes of Health (Acute Lung Injury SCCOR Grant # P050 HL 73994-01). Dr. Needham is supported by a Clinician-Scientist Award from the Canadian Institutes of Health Research. Dr. Dennison is supported by the Mentored Patient-Oriented Research Career Development Award from the National Institutes of Health (K23 NR009193). The funding bodies had no role in the study
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