Strategies to improve retention in randomised trials: a Cochrane systematic review and meta-analysis
Open accessAbstract
Objective: To quantify the effect of strategies to improve retention in randomised trials. Design: Systematic review and meta-analysis. Data sources: Sources searched: MEDLINE, EMBASE, PsycINFO, DARE, CENTRAL, CINAHL, C2-SPECTR, ERIC, PreMEDLINE, Cochrane Methodology Register, Current Controlled Trials metaRegister, WHO trials platform, Society for Clinical Trials (SCT) conference proceedings and a survey of all UK clinical trial research units. Review methods: Included trials were randomised evaluations of strategies to improve retention embedded within host randomised trials. The primary outcome was retention of trial participants. Data from trials were pooled using the fixed-effect model. Subgroup analyses were used to explore the heterogeneity and to determine whether there were any differences in effect by the type of strategy. Results: 38 retention trials were identified. Six broad types of strategies were evaluated. Strategies that increased postal questionnaire responses were: adding, that is, giving a monetary incentive (RR 1.18; 95% CI 1.09 to 1.28) and higher valued incentives (RR 1.12; 95% CI 1.04 to 1.22). Offering a monetary incentive, that is, an incentive given on receipt of a completed questionnaire, also increased electronic questionnaire response (RR 1.25; 95% CI 1.14 to 1.38). The evidence for shorter questionnaires (RR 1.04; 95% CI 1.00 to 1.08) and questionnaires relevant to the disease/condition (RR 1.07; 95% CI 1.01 to 1.14) is less clear. On the basis of the results of single trials, the following strategies appeared effective at increasing questionnaire response: recorded delivery of questionnaires (RR 2.08; 95% CI 1.11 to 3.87); a ‘package’ of postal communication strategies (RR 1.43; 95% CI 1.22 to 1.67) and an open trial design (RR 1.37; 95% CI 1.16 to 1.63). There is no good evidence that the following strategies impact on trial response/retention: adding a non-monetary incentive (RR=1.00; 95% CI 0.98 to 1.02); offering a non-monetary incentive (RR=0.99; 95% CI 0.95 to 1.03); ‘enhanced’ letters (RR=1.01; 95% CI 0.97 to 1.05); monetary incentives compared with offering prize draw entry (RR=1.04; 95% CI 0.91 to 1.19); priority postal delivery (RR=1.02; 95% CI 0.95 to 1.09); behavioural motivational strategies (RR=1.08; 95% CI 0.93 to 1.24); additional reminders to participants (RR=1.03; 95% CI 0.99 to 1.06) and questionnaire question order (RR=1.00, 0.97 to 1.02). Also based on single trials, these strategies do not appear effective: a telephone survey compared with a monetary incentive plus questionnaire (RR=1.08; 95% CI 0.94 to 1.24); offering a charity donation (RR=1.02, 95% CI 0.78 to 1.32); sending sites reminders (RR=0.96; 95% CI 0.83 to 1.11); sending questionnaires early (RR=1.10; 95% CI 0.96 to 1.26); longer and clearer questionnaires (RR=1.01, 0.95 to 1.07) and participant case management by trial assistants (RR=1.00; 95% CI 0.97 to 1.04). Conclusions: Most of the trials evaluated questionnaire response rather than ways to improve participants return to site for follow-up. Monetary incentives and offers of monetary incentives increase postal and electronic questionnaire response. Some strategies need further evaluation. Application of these results would depend on trial context and follow-up procedures.
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It is important to consider the potential impact on retention rates, which often presents a significant challenge in RCTs.
“It is, however, important to consider the potential impact on retention rates, which often presents a significant challenge in RCTs [81].”
From Blinding outcome assessors in randomised controlled trials of psychological interventions: how is it done? A narrative review (2026) · cites this paper as [81]
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“It is, however, important to consider the potential impact on retention rates, which often presents a significant challenge in RCTs [81].”
- Authors
- Brueton, V. C., Tierney, J. F., Stenning, S., Meredith, S., Harding, S., Nazareth, I., & Rait, G.
- Affiliations
- MRC Clinical Trials Unit at UCL (GB)
- MRC/CSO Social and Public Health Sciences Unit (GB)
- University College London (GB)
- Corresponding author
- Brueton, V C
- Venue
- BMJ Open
- Publisher
- BMJ
- Published
- 2014-02
- Volume
- 4
- Issue
- 2
- Pages
- e003821
- ISSN
- 2044-6055 (ISSN-L)
- PMC
- PMC3918995
- OpenAlex
- W2110140939
- Cited by
- 253
- References
- 46
- Citations by year
- 2026: 8 · 2025: 19 · 2024: 21 · 2023: 20 · 2022: 20 · 2021: 33 · 2020: 29 · 2019: 29 · 2018: 21 · 2017: 16 · 2016: 22 · 2015: 12 · 2014: 2
- FWCI
- 5.72
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Licence
- cc-by
- Locations
- BMJ Open (publishedVersion, cc-by)
- Europe PMC (PubMed Central) (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- ENLIGHTEN (Jurnal Bimbingan dan Konseling Islam) (acceptedVersion)
- UCL Discovery (University College London) (submittedVersion, cc-by)
- Research Portal (King's College London) (submittedVersion, cc-by)
- HighWire Press Open Archive (submittedVersion)
- Funders
- Medical Research Council (MC_EX_G0800814, MC_EX_G0701943, PHSRN 30)
- Topics
- Social Sciences › Sociology and Political Science › Survey Methodology and Nonresponse
- Health Sciences › Medicine › Public Health, Environmental and Occupational Health › Ethics in Clinical Research
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
- Keywords
- trial participant retention, randomised trials, survey responses, postal questionnaires, electronic questionnaires, financial incentives, non-monetary incentives, questionnaire length, retention strategies, attrition, participant dropout, participant retention, participant recruitment
- MeSH terms
- Humans, Patient Compliance, Patient Dropouts, Randomized Controlled Trials as Topic, Research Subjects
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