ArticleBMC medical research methodology2005
A priori postulated and real power in cluster randomized trials: mind the gap.
Article in BMC medical research methodology, 2005. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 11 papers.
What it found
Each row is one number read from the abstract, on the scale the paper reported it, with its interval. Left of the dashed line favours the treatment, right favours the comparator. Under each row is the sentence it came from. New to these charts? A ten-minute tutorial.
The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.
The trial behind it
Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.
Neither the registry nor the abstract names a trial number. If this is a trial report, that itself is worth knowing.
Who cites it
11 citing papers in PubMed.
- Ethical implications of excessive cluster sizes in cluster randomised trials.BMJ quality & safety · 2018Trial
- ARTIST (osteoarthritis intervention standardized) study of standardised consultation versus usual care for patients with osteoarthritis of the knee in primary care in France: pragmatic randomised controlled trial.BMJ (Clinical research ed.) · 2009Trial
- The HOPE program: protocol for a stratified cluster randomized controlled trial to prevent psychoactive substance use and promote health in Moroccan middle school students.Addiction science & clinical practice · 2026Article
- Power analysis for concurrent balanced or imbalanced multiple-intervention stepped wedge design: a simulation-based approach.BMC medical research methodology · 2025Article
- Cluster-Randomized Studies.Deutsches Arzteblatt international · 2018Review
- How to design efficient cluster randomised trials.BMJ (Clinical research ed.) · 2017Article
- The Effects of Skill Training on Social Workers' Professional Competences in Norway: Results of a Cluster-Randomised Study.British journal of social work · 2016Article
- Sample size calculations for stepped wedge and cluster randomised trials: a unified approach.Journal of clinical epidemiology · 2016Article
- Sample size calculations for cluster randomised controlled trials with a fixed number of clusters.BMC medical research methodology · 2011Article
- Planning a cluster randomized trial with unequal cluster sizes: practical issues involving continuous outcomes.BMC medical research methodology · 2006Article
- Intraclass correlation coefficients typical of cluster-randomized studies: estimates from the Robert Wood Johnson Prescription for Health projects.Annals of family medicineArticle
Corrections and comments
PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.
Authors and funding
3 authors.
Funding
No grant is acknowledged in the PubMed record.
Abstract
backgroundCluster randomization design is increasingly used for the evaluation of health-care, screening or educational interventions. The intraclass correlation coefficient (ICC) defines the clustering effect and be specified during planning. The aim of this work is to study the influence of the ICC on power in cluster randomized trials.
methodsPower contour graphs were drawn to illustrate the loss in power induced by an underestimation of the ICC when planning trials. We also derived the maximum achievable power given a specified ICC.
resultsThe magnitude of the ICC can have a major impact on power, and with low numbers of clusters, 80% power may not be achievable.
conclusionUnderestimating the ICC during planning cluster randomized trials can lead to a seriously underpowered trial. Publication of a priori postulated and a posteriori estimated ICCs is necessary for a more objective reading: negative trial results may be the consequence of a loss of power due to a mis-specification of the ICC.
Indexed as
Identifiers
What OpenQuestion holds
Registered trials
Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.