Cited by 224Statistical Methods in Clinical TrialsMeta-analysis and systematic reviewsHealth Policy Implementation Science

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Internal and external validity of cluster randomised trials: systematic review of recent trials

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Eldridge, Sandra, Ashby, Deborah, Bennett, Catherine, Wakelin, Melanie, Feder, Gene·2008·BMJ

DOI 10.1136/bmj.39517.495764.25PMC PMC2323095

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Abstract

OBJECTIVES: To assess aspects of the internal validity of recently published cluster randomised trials and explore the reporting of information useful in assessing the external validity of these trials. DESIGN: Review of 34 cluster randomised trials in primary care published in 2004 and 2005 in seven journals (British Medical Journal, British Journal of General Practice, Family Practice, Preventive Medicine, Annals of Internal Medicine, Journal of General Internal Medicine, Pediatrics). DATA SOURCES: National Library of Medicine (Medline) via PubMed. DATA EXTRACTION: To assess aspects of internal validity we extracted data on appropriateness of sample size calculations and analyses, methods of identifying and recruiting individual participants, and blinding. To explore reporting of information useful in assessing external validity we extracted data on cluster eligibility, cluster inclusion and retention, cluster generalisability, and the feasibility and acceptability of the intervention to health providers in clusters. RESULTS: 21 (62%) trials accounted for clustering in sample size calculations and 30 (88%) in the analysis; about a quarter were potentially biased because of procedures surrounding recruitment and identification of patients; individual participants were blind to allocation status in 19 (56%) and outcome assessors were blind in 15 (44%). In almost half the reports, information relating to generalisability of clusters was poorly reported, and in two fifths there was no information about the feasibility and acceptability of the intervention. CONCLUSIONS: Cluster randomised trials are essential for evaluating certain types of interventions. Issues affecting their internal validity, such as appropriate sample size calculations and analysis, have been widely disseminated and are now better addressed by researchers. Blinding of those identifying and recruiting patients to allocation status is recommended but is not always carried out. There may be fewer barriers to internal validity in trials in which individual participants are not recruited. External validity seems poorly addressed in many trials, yet is arguably as important as internal validity in judging quality as a basis for healthcare intervention.

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Authors: Eldridge, S., Ashby, D., Bennett, C., Wakelin, M., & Feder, G.
Affiliations: Queen Mary University of London (GB)
Corresponding author: Eldridge, Sandra
ORCID: Eldridge, Sandra
Ashby, Deborah
Feder, Gene
Venue: BMJ
Publisher: BMJ
Published: 2008-03-25
Volume: 336
Issue: 7649
Pages: 876-880
ISSN: 1756-1833 (ISSN-L)
0959-8138
DOI: 10.1136/bmj.39517.495764.25
PMC: PMC2323095
OpenAlex: W2047660576
Cited by: 224
References: 41
Citations by year: 2026: 6 · 2025: 14 · 2024: 8 · 2023: 12 · 2022: 5 · 2021: 15 · 2020: 6 · 2019: 8 · 2018: 11 · 2017: 11 · 2016: 16 · 2015: 7 · 2014: 9 · 2013: 20 · 2012: 23
FWCI: 2.55
Type: journal article
Language: en
Open access: bronze
doi.org
Licence: www.bmj.org/licenses/tdm/1.0/terms-and-conditions.html (tdm)
Locations: BMJ (publishedVersion)
PubMed Central (publishedVersion)
PubMed (publishedVersion)
HighWire Press Open Archive (submittedVersion)
Bristol Research (University of Bristol) (submittedVersion)
Explore Bristol Research (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: internal validity, generalizability, trial reporting quality, sample size determination, blinding, participant recruitment, feasibility and acceptability
MeSH terms: Reproducibility of Results, Cluster Analysis, Randomized Controlled Trials as Topic, Sample Size

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Internal and external validity of cluster randomised trials: systematic review of recent trials

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