How do trial teams plan for retention during the design stage of the trial? A scoping review protocol

Retention remains a major challenge for many clinical trials. The SPIRIT guidelines state the following information on retention should be included in the trial protocol "Plans to promote participant retention and complete follow-up, including list of any outcome data to be collected for participants who discontinue or deviate from intervention protocols". This guidance shows the importance of planning retention methods and handling missing data as this can impact how the results of the trial are interpreted. The most recent Cochrane review of strategies to improve retention in clinical trials highlighted that some trials implemented multiple retention strategies and we questioned whether the use of multiple strategies was planned at the design stage and included in the protocol or are strategies implemented when retention becomes an issue within the trial. The purpose of our scoping review is to establish if and how trial teams prepare for retention at the design phase of clinical trials.

We will follow the methodological framework and guidelines for scoping reviews outlined by the Joanna Briggs Institute. We will search MEDLINE/PubMed, Scopus, EMBASE, CINAHL (EBSCO), and Web of Science. A comprehensive search strategy for PubMed was developed in collaboration with an experienced research librarian. We will include protocols for phase 2, 3, and 4 RCTs as well as pilot and feasibility studies. The screening process will involve two reviewers. EM will independently screen all titles and abstracts. FS will screen 10% of the overall search output, and where necessary full protocol texts will be screened to determine eligibility. We will randomly sample eligible protocols to ensure the protocols represent a variety of trial and intervention types. Data will be extracted from each protocol and the results will be synthesised. The analysis will be qualitative using a narrative summary and descriptive statistics where appropriate.

The scoping review will help trial methodologists better understand if retention strategies are planned for during the design stage of the trial contributing to the PRioRiTy II unanswered question "How should people who run trials plan for retention during their funding application and creation of the trial (protocol development)?".