Developing an online, searchable database to systematically map and organise current literature on retention research (ORRCA2)

Anna Kearney* (Corresponding Author), Polly-Anna Ashford, Laura Butlin, Thomas Conway, William J. Cragg, Declan Devane, Heidi Gardner, Daisy Gaunt, Katie Gillies, Nicola L Harman, Andrew Hunter, J Athene Lane, Catherine McWilliams, Louise.l. Murphy, Carrie O’Nions, Edward N Stanhope, Akke Vellinga, Paula R. Williamson, Carrol Gamble

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)
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Background: Addressing recruitment and retention challenges in trials is a key priority for methods research, but navigating the literature is difficult and time-consuming. In 2016, ORRCA ( launched a free, searchable database of recruitment research that has been widely accessed and used to support the update of systematic reviews and the selection of recruitment strategies for clinical trials. ORRCA2 aims to create a similar database to map the growing volume and importance of retention research.

Methods: Searches of Medline (Ovid), CINAHL, PsycINFO, Scopus, Web of Science Core Collection and the Cochrane Library, restricted to English language and publications up to the end of 2017. Hand searches of key systematic reviews were undertaken and randomised evaluations of recruitment interventions within the ORRCA database on 1 October 2020 were also reviewed for any secondary retention outcomes. Records were screened by title and abstract before obtaining the full text of potentially relevant articles. Studies reporting or evaluating strategies, methods and study designs to improve retention within healthcare research were eligible. Case reports describing retention challenges or successes and studies evaluating participant reported reasons for withdrawal or losses were also included. Studies assessing adherence to treatments, attendance at appointments outside of research and statistical analysis methods for missing data were excluded. Eligible articles were categorised into one of the following evidence types: randomised evaluations, non-randomised evaluations, application of retention strategies without evaluation and observations of factors affecting retention. Articles were also mapped against a retention domain framework. Additional data were extracted on research outcomes, methods and host study context.

Results: Of the 72,904 abstracts screened, 4,364 full texts were obtained, and 1,167 articles were eligible. Of these, 165 (14%) were randomised evaluations, 99 (8%) non-randomised evaluations, 319 (27%) strategies without evaluation and 584 (50%) observations of factors affecting retention. Eighty-four percent (n = 979) of studies assessed the numbers of participants retained, 27% (n = 317) assessed demographic differences between retained and lost participants, while only 4% (n = 44) assessed the cost of retention strategies. The most frequently reported domains within the 165 studies categorised as 'randomised evaluations of retention strategies' were participant monetary incentives (32%), participant reminders and prompts (30%), questionnaire design (30%) and data collection location and method (26%).

Conclusion: ORRCA2 builds on the success of ORRCA extending the database to organise the growing volume of retention research. Less than 15% of articles were randomised evaluations of retention strategies. Mapping of the literature highlights several areas for future research such as the role of research sites, clinical staff and study design in enhancing retention. Future studies should also include cost-benefit analysis of retention strategies.
Original languageEnglish
Pages (from-to)71-80
Number of pages10
JournalClinical Trials
Issue number1
Early online date24 Oct 2021
Publication statusPublished - Feb 2022

Bibliographical note

The authors acknowledge the collaborative nature of this project which wouldn’t have been possible without the following people (in alphabetical order): Grant co-applicants: Sophia Ananiadou, William Cragg, Declan Devane, Carrol Gamble,
Katie Gillies, Nicola Harman, Anna Kearney, Athene Lane and Paula Williamson; ORRCA/ORRCA2 database infrastructure: Duncan Appelbe, Richard Crew, Keith Kennedy and Robert Sherman; Researchers involved in abstract screening: Polly-Anna Ashford, Lucy Beasant, Laura Butlin, Thomas Conway, Rachael Cooper, Hannah Delaney, Sinead Duane, Adel El Feky, Daisy Gaunt, Amy Humphries,
8 Clinical Trials 00(0) Andrew Hunter, Anna Kearney, Sarah Lenson, Catherine
McWilliams, Louise Murphy, Rumana S. N. Newlands, Carrie O’Nions, Karen Scott, Edward N Stanhope, Victoria Yorke-Edwards and Akke Vellinga; Researchers involved in full-text review: Polly-Anna Ashford, Thomas Conway, Sinead Duane, Adel El Feky, Heidi Gardner, Daisy Gaunt, Andrew Hunter, Anna Kearney, Catherine McWilliams, Louise Murphy, Carrie O’Nions, Edward N Stanhope and
Akke Vellinga; A full list of current and past reviewers for ORRCA and ORRCA2 is available at Further information about joining the review team can be obtained by contacting us via the website or social media (@ORRCA_rct).

The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This study was funded by Medical Research Council Hub for Trials Methodology Research Network (Grant Ref N101) and the Health Research Board Trials Methodology Research Network


  • Participant retention
  • clinical trials
  • trials methodology
  • attrition
  • Literature review


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