Research article summary (published 13 Aug 2009):

Varying cluster sizes in trials with clusters in one treatment arm: sample size adjustments when testing treatment effects with linear mixed models.

Full Abstract

Trials in which treatments induce clustering of observations in one of two treatment arms, such as when comparing group therapy with pharmacological treatment or with a waiting-list group, are examined with respect to the efficiency loss caused by varying cluster sizes. When observations are (approximately) normally distributed, treatment effects can be estimated and tested through linear mixed model analysis. For maximum likelihood estimation, the asymptotic relative efficiency of unequal versus equal cluster sizes is derived. In an extensive Monte Carlo simulation for small sample sizes, the asymptotic relative efficiency turns out to be accurate for the treatment effect, but less accurate for the random intercept variance. For the treatment effect, the efficiency loss due to varying cluster sizes rarely exceeds 10 per cent, which can be regained by recruiting 11 per cent more clusters for one arm and 11 per cent more persons for the other. For the intercept variance the loss can be 16 per cent, which requires recruiting 19 per cent more clusters for one arm, with no additional recruitment of subjects for the other arm. Copyright 2009 John Wiley & Sons, Ltd.

Author information

Author/s: Candel, Math J J M (MJ); Van Breukelen, Gerard J P (GJ);

Affiliation: Department of Methodology and Statistics, Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands. Math.Candel(-atsign-)Stat.unimaas.nl

Journal and publication information

Publication Type: Journal Article

Journal: Statistics in medicine (Stat Med), published in England. (Language: eng)

Reference: 2009-Aug; vol 28 (issue 18) : pp 2307-24

Dates: Created 2009/07/14; Completed 2009/10/01;

PMID: 19472169, status: MEDLINE (last retrieval date: 10/1/2009, IMS Date: )

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

External Links for this article
(including full text providers, if available):

Click Electronic Full-text Provider Links to see options for finding the electronic full text links to this article. Note there may be a subscription or fee required for access to the full text. See our FAQ for information on finding FREE full text articles.

This article may also be located in paper journal collections available in many libraries. Use the Journal and Publication Information above to find the full article.

MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Biometry Clinical Trials as Topic - statistics & numerical data Cluster Analysis Computer Simulation Humans Likelihood Functions

Likelihood Functions Linear Models Monte Carlo Method Randomized Controlled Trials as Topic - statistics & numerical data Sample Size Treatment Outcome

Related articles

These are the highest related articles currently in the database:

• Inference using conditional logistic regression with missing covariates. 27 Feb 1998
• Approximate hierarchical modelling of discrete data in epidemiology. 27 Feb 1998
• Adaptive designs from the viewpoint of an academic biostatistician. 30 Jul 2006
• Adjusting for regression effect in uncontrolled studies. 27 Feb 2001
• A sample size formula for the supremum log-rank statistic. 27 Feb 2005
• Tests for the analysis of variance of crossover designs with correlated errors. 30 May 1996
• Properties of a nonparametric test for early comparison of treatments in clinical trials in the presence of surrogate endpoints. 29 Nov 1999
• Adaptive sample size calculations in group sequential trials. 29 Nov 1999
• Design of multi-centre trials with binary response. 28 Aug 2006
• A unified method for monitoring and analysing controlled trials. 28 Sep 1994

See 100+ related articles.

Related Article Map

Legend: - FREE Full text Article. - Abstract only. - Title only. More help.

See a large map of 100+ related articles.