Methodological bias in cluster randomised trials
Open accessAbstract
Background: Cluster randomised trials can be susceptible to a range of methodological problems. These problems are not commonly recognised by many researchers. In this paper we discuss the issues that can lead to bias in cluster trials. Methods: We used a sample of cluster randomised trials from a recent review and from a systematic review of hip protectors. We compared the mean age of participants between intervention groups in a sample of 'good' cluster trials with a sample of potentially biased trials. We also compared the effect sizes, in a funnel plot, between hip protector trials that used individual randomisation compared with those that used cluster randomisation. Results: There is a tendency for cluster trials, with evidence methodological biases, to also show an age imbalance between treatment groups. In a funnel plot we show that all cluster trials show a large positive effect of hip protectors whilst individually randomised trials show a range of positive and negative effects, suggesting that cluster trials may be producing a biased estimate of effect. Conclusion: Methodological biases in the design and execution of cluster randomised trials is frequent. Some of these biases associated with the use of cluster designs can be avoided through careful attention to the design of cluster trials. Firstly, if possible, individual allocation should be used. Secondly, if cluster allocation is required, then ideally participants should be identified before random allocation of the clusters. Third, if prior identification is not possible, then an independent recruiter should be used to recruit participants.
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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 [16]
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References 22 · Cited by 310
Research works printed but not linked: 3
- Schulz KF Chalmers I Grimes DA Altman DG Assessing the quality of randomization from reports of controlled trials in obstetrics and gynaecology journals JAMA 1994 272 125 28 8015122 10.1001/jama.272.2.125 · DOI
- Molloy DW Guyatt GH Russo R Goeree R O'Brien BJ Systematic implementation of and advance directive program in nursing homes: A randomized controlled trial JAMA 2000 283 1437 44 10732933 10.1001/jama.283.11.1437 · DOI
- Parker MJ Gillespie LD Gillespie WJ Hip Protectors for preventing hip fractures in the elderly (Cochrane Review) The Cochrane Library 2004 Chichester, UK: John Wiley & Sons, Ltd 15266444
- Authors
- Hahn, S., Puffer, S., Torgerson, D. J., & Watson, J.
- Affiliations
- Seoul National University (KR)
- Corresponding author
- Torgerson, David J
- Venue
- BMC Medical Research Methodology
- Published
- 2005-03-02
- Volume
- 5
- Issue
- 1
- Pages
- 10-10
- ISSN
- 1471-2288 (ISSN-L)
- PMC
- PMC554774
- OpenAlex
- W1561225387
- Cited by
- 310
- References
- 22
- Citations by year
- 2026: 1 · 2025: 10 · 2024: 14 · 2023: 10 · 2022: 18 · 2021: 15 · 2020: 59 · 2019: 15 · 2018: 15 · 2017: 10 · 2016: 18 · 2015: 19 · 2014: 22 · 2013: 22 · 2012: 9
- FWCI
- 6.90
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Locations
- BMC Medical Research Methodology (publishedVersion, cc-by)
- Europe PMC (PubMed Central) (publishedVersion, cc-by)
- PubMed Central (publishedVersion, cc-by)
- PubMed (publishedVersion)
- White Rose Research Online (University of Leeds, The University of Sheffield, University of York) (acceptedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
- 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
- methodological bias, cluster allocation, hip protectors, effect size estimation, trial design
- MeSH terms
- Age Factors, Hip Fractures, Humans, Informed Consent, Periodicals as Topic, Protective Devices, Research Design, Selection Bias, Cluster Analysis, Randomized Controlled Trials as Topic, Sample Size, Patient Selection, Refusal to Participate
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