Design and analysis of clinical trials with clustering effects due to treatment

Roberts, Chris; Roberts, Stephen A

doi:10.1191/1740774505cn076oa

Cited by 299Statistical Methods in Clinical TrialsStatistical Methods and Bayesian InferenceMeta-analysis and systematic reviews

Design and analysis of clinical trials with clustering effects due to treatment

Roberts, Chris, Roberts, Stephen A·2005·Clinical Trials

DOI 10.1191/1740774505cn076oa

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Abstract

Where patients receive therapy as a group, there are good theoretical reasons to believe that variation in the outcome will be smaller for patients treated in the same group than for patients treated in different groups. Similarly, where different therapists treat different groups of patients, outcome for patients treated by the same therapist may differ less than outcome for patients treated by different therapists. Clinical trials evaluating such therapies need to consider this potential lack of independence. As with cluster-randomized trials, this has implications for the precision of treatment effects estimates and statistical power. There are nevertheless differences between clustering due to the organization of treatment and that due to randomization. In cluster-randomized trials the distribution of cluster sizes in each treatment arm should be similar as a consequence of randomization unless there is differential loss to follow-up. With clustering due to therapy group or therapist, cluster size may differ systematically between treatment arms, due to size of therapy groups or differing health professional caseload. Intra-cluster correlation may also differ between treatment arms. The implications of differential cluster size and intracluster correlation for design and analysis will be illustrated by data from two trials, the first comparing nurse practitioner care with general practitioner care, and the second comparing a group therapy with individual treatment as usua…

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An allocation ratio of 2:1 (intervention: treatment as usual) was used to allow for potential clustering effects in the intervention arm.
“To allow for potential clustering effects in the intervention arm we used an allocation ratio of 2:1 (intervention: treatment as usual).18”
From Clinical effectiveness of a manual based coping strategy programme (START, STrAtegies for RelaTives) in promoting the mental health of carers of family members with dementia: pragmatic randomised controlled trial (2013) · cites this paper as [18]
Based on an average cluster size of 13 evaluable participants and a therapist intraclass correlation coefficient of 0.05, 364 evaluable patients at 3 months would provide 92% power to detect the difference with a two-sample test and a significance level of 5%.
“Based on an average cluster size of 13 evaluable participants (those completing 3 months follow-up), and a therapist (health professional delivering the intervention) intraclass correlation coefficient of 0.05(ref. 30) in the intervention arm, a total of 364 evaluable patients at 3 months would provide 92% power to detect such a difference with a two-sample test and a significance level of 5%.31”
From A brief intervention for weight control based on habit-formation theory delivered through primary care: results from a randomised controlled trial (2017) · cites this paper as [31]

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Article
(2016)
Effect of imbalance and intracluster correlation coefficient in cluster randomized trials with binary outcomes
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Self-citation

Authors: Roberts, C., & Roberts, S. A.
Affiliations: University of Manchester (GB)
Corresponding author: Roberts, Chris
ORCID: Roberts, Stephen A
Venue: Clinical Trials
Publisher: SAGE Publications
Published: 2005-04
Volume: 2
Issue: 2
Pages: 152-162
ISSN: 1740-7745 (ISSN-L)
1740-7753
DOI: 10.1191/1740774505cn076oa
OpenAlex: W2093029291
Cited by: 299
References: 30
Citations by year: 2026: 8 · 2025: 14 · 2024: 16 · 2023: 18 · 2022: 14 · 2021: 23 · 2020: 33 · 2019: 23 · 2018: 13 · 2017: 11 · 2016: 14 · 2015: 12 · 2014: 22 · 2013: 12 · 2012: 17
FWCI: 4.50
Type: journal article
Language: en
Open access: closed
Licence: journals.sagepub.com/page/policies/text-and-data-mining-license (tdm)
Locations: Clinical Trials (publishedVersion)
PubMed (publishedVersion)
Research Explorer (The University of Manchester) (submittedVersion)
Topics: Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods and Bayesian Inference
Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
Keywords: cluster effect, group therapy, therapist effects, intra-cluster correlation, statistical power, sample size, general practitioner care, simulation study
MeSH terms: Data Interpretation, Statistical, Group Processes, Humans, Nurse Practitioners, Physicians, Family, Research Design, Statistics as Topic, Cluster Analysis, Randomized Controlled Trials as Topic, Treatment Outcome, Sample Size

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Design and analysis of clinical trials with clustering effects due to treatment

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