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BMC Medical Research Methodology
Published in: BMC Medical Research Methodology 1/2006

Open Access 01-12-2006 | Research article

Intra-cluster correlation coefficients in adults with diabetes in primary care practices: the Vermont Diabetes Information System field survey

Authors: Benjamin Littenberg, Charles D MacLean

Published in: BMC Medical Research Methodology | Issue 1/2006

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Abstract

Background

Proper estimation of sample size requirements for cluster-based studies requires estimates of the intra-cluster correlation coefficient (ICC) for the variables of interest.

Methods

We calculated the ICC for 112 variables measured as part of the Vermont Diabetes Information System, a cluster-randomized study of adults with diabetes from 73 primary care practices (the clusters) in Vermont and surrounding areas.

Results

ICCs varied widely around a median value of 0.0185 (Inter-quartile range: 0.006, 0.037). Some characteristics (such as the proportion having a recent creatinine measurement) were highly associated with the practice (ICC = 0.288), while others (prevalence of some comorbidities and complications and certain aspects of quality of life) varied much more across patients with only small correlation within practices (ICC<0.001).

Conclusion

The ICC values reported here may be useful in designing future studies that use clustered sampling from primary care practices.
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Metadata
Title
Intra-cluster correlation coefficients in adults with diabetes in primary care practices: the Vermont Diabetes Information System field survey
Authors
Benjamin Littenberg
Charles D MacLean
Publication date
01-12-2006
Publisher
BioMed Central
Published in
BMC Medical Research Methodology / Issue 1/2006
Electronic ISSN: 1471-2288
DOI
https://doi.org/10.1186/1471-2288-6-20

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