Bias in recruitment to cluster randomized trials: a review of recent publications
Abstract
Objectives To assess recruitment bias and the techniques employed to counter this problem in a recent selection of published cluster randomized trials. Design Review of 24 cluster trials published in 2008 in four leading medical journals. Data extraction Studies were assessed by four reviewers to identify if an alternative design could have been employed using individual randomization. Data were also extracted on the randomization procedure and the likelihood of this introducing bias to the selection of participants into the study. Results Of the 24 trials, eight could have used individual randomization as an alternative to cluster allocation. Seven studies could have recruited participants prior to cluster randomization but did not. In eight studies where recruitment bias was possible, more than half (five) demonstrated some evidence of differential recruitment rates. Conclusions Many cluster trials published in leading medical journals are not clear in their justification for the design. We also found significant proportions of cluster trials used suboptimal designs that increase their risk of introducing selection bias. Better design of cluster trials is possible and should be adopted.
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Cluster-randomized designs are known to be at increased risk of bias compared to the individually randomized design.
“Cluster-randomized designs are known to be at increased risk of bias compared to the individually randomized design [1], [2], [7], [10], [13], [16], [28], [37].”
From Cluster randomized trials of individual-level interventions were at high risk of bias (2021) · cites this paper as [2]
Knowledge of treatment condition at the time of patient recruitment is known to be a risk factor for differential identification and recruitment of participants across treatment arms, unless recruitment and identification are conducted by someone blind to the treatment allocation or the inclusion criteria are broad.
“Knowledge of treatment condition at the time of patient recruitment is known to be a risk factor for differential identification and recruitment of participants across treatment arms [1,14,16,37], unless recruitment and identification are conducted by someone blind to the treatment allocation or the inclusion criteria are broad [2,11,14].”
From Cluster randomized trials of individual-level interventions were at high risk of bias (2021) · cites this paper as [2]
Methodological reviews have identified that many cluster trials are at risk of these identification and recruitment biases because they recruit participants with knowledge of allocated treatment and this often manifests in baseline imbalances.
“Methodological reviews have identified that many cluster trials are at risk of these identification and recruitment biases because they recruit participants with knowledge of allocated treatment and this often manifests in baseline imbalances [1,2,28].”
From Cluster randomized trials of individual-level interventions were at high risk of bias (2021) · cites this paper as [2]
Others have assessed about 40% of cluster trials to be at risk of these types of biases; and sometimes this has been reported to be somewhat lower despite including many trials with post randomization recruitment.
“Others have assessed about 40% of cluster trials to be at risk of these types of biases [2,7,28]; and sometimes this has been reported to be somewhat lower despite including many trials with post randomization recruitment [10,13].”
From Cluster randomized trials of individual-level interventions were at high risk of bias (2021) · cites this paper as [2]
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References 57 · Cited by 62
- Authors
- Brierley, G., Brabyn, S., Torgerson, D., & Watson, J.
- Affiliations
- University of Bristol (GB)
- University of York (GB)
- Corresponding author
- Brierley, Gwen
- Venue
- Journal of Evaluation in Clinical Practice
- Publisher
- Wiley
- Published
- 2011-06-20
- Volume
- 18
- Issue
- 4
- Pages
- 878-886
- ISSN
- 1356-1294 (ISSN-L)
- 1365-2753
- OpenAlex
- W1958931973
- Cited by
- 62
- References
- 57
- Citations by year
- 2026: 2 · 2025: 3 · 2024: 1 · 2023: 6 · 2022: 4 · 2021: 7 · 2020: 7 · 2019: 5 · 2018: 7 · 2017: 4 · 2016: 3 · 2015: 2 · 2014: 2 · 2013: 5 · 2012: 3
- FWCI
- 3.07
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Journal of Evaluation in Clinical Practice (publishedVersion)
- PubMed (publishedVersion)
- Bristol Research (University of Bristol) (publishedVersion)
- Topics
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
- Health Sciences › Health Professions › General Health Professions › Health Policy Implementation Science
- Keywords
- recruitment bias, selection bias, cluster allocation, participant recruitment
- MeSH terms
- Female, Humans, Male, Bias, Randomized Controlled Trials as Topic, Patient Selection
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