Evidence map›Paper›PMID 16611355›Full record

ArticleBMC medical research methodology2006

Planning a cluster randomized trial with unequal cluster sizes: practical issues involving continuous outcomes.

Lydia Guittet, Philippe Ravaud, Bruno Giraudeau

Registry-linked trialAbstract readComparative Study
PubMed Full text at PMC Publisher
In one paragraph

Article in BMC medical research methodology, 2006. The graph could read no effect estimate from its abstract, so it casts no vote on the map. It is linked to trial NCT01436331 (A Pragmatic Cluster Randomized Controlled Trial of a Multi-element Psychosocial Intervention for Early Psychosis in a 10 Million Inhabitant Catchment Area Aimed to Measure the Treatment's Feasibility and Effectiveness), which is not on this map. Cited by 25 papers, 1 of them a synthesis that pooled it.

0numbers the graph read from it
0cells of the map it votes in
25citing papers in PubMed, 1 pooled it
–field-weighted citation impact
1 · What the graph read from it

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.

2 · The registry

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.

NCT01436331 nacompletednot on this mapstarted 2010, after this paper: background citation

A Pragmatic Cluster Randomized Controlled Trial of a Multi-element Psychosocial Intervention for Early Psychosis in a 10 Million Inhabitant Catchment Area Aimed to Measure the Treatment's Feasibility and Effectiveness: GET UP-PIANO Trial

TypeinterventionalSponsorUniversita di VeronaRan2010 to 2012Enrolled626ConditionsPsychosisArmsTreatment As Usual (TAU), TAU+CBT for pts+Family Intervention+CM.
3 · Its place in the literature

Who cites it

25 citing papers in PubMed, 1 synthesis or guideline pooled it.

  1. Do community health worker interventions improve rates of screening mammography in the United States? A systematic review.Cancer epidemiology, biomarkers & prevention : a publication of the American Association for Cancer Research, cosponsored by the American Society of Preventive Oncology · 2011
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4 · The record

Corrections and comments

PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.

5 · Who and what money

Authors and funding

3 authors.

Lydia GuittetDépartement d'Epidémiologie, Biostatistique et Recherche Clinique, Groupe Hospitalier Bichat-Claude Bernard (AP-HP), Université Xavier Bichat, Paris, France. guittetl@free.fr
Philippe Ravaud
Bruno Giraudeau

Funding

No grant is acknowledged in the PubMed record.

6 · The paper itself

Abstract

backgroundCluster randomization design is increasingly used for the evaluation of health-care, screening or educational interventions. At the planning stage, sample size calculations usually consider an average cluster size without taking into account any potential imbalance in cluster size. However, there may exist high discrepancies in cluster sizes.

methodsWe performed simulations to study the impact of an imbalance in cluster size on power. We determined by simulations to which extent four methods proposed to adapt the sample size calculations to a pre-specified imbalance in cluster size could lead to adequately powered trials.

resultsWe showed that an imbalance in cluster size can be of high influence on the power in the case of severe imbalance, particularly if the number of clusters is low and/or the intraclass correlation coefficient is high. In the case of a severe imbalance, our simulations confirmed that the minimum variance weights correction of the variation inflaction factor (VIF) used in the sample size calculations has the best properties.

conclusionPublication of cluster sizes is important to assess the real power of the trial which was conducted and to help designing future trials. We derived an adaptation of the VIF from the minimum variance weights correction to be used in case the imbalance can be a priori formulated such as "a proportion (gamma) of clusters actually recruit a proportion (tau) of subjects to be included (gamma < or = tau)".

Indexed as

Cluster AnalysisSample SizeAnalysis of VarianceBiasConfidence IntervalsData Interpretation, StatisticalHumansRandomized Controlled Trials as TopicResearch DesignTreatment Outcome

Identifiers

PMID16611355
PMCPMC1513250

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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.