Observed intra-cluster correlation coefficients in a cluster survey sample of patient encounters in general practice in Australia

Knox, SA; Chondros, P

Observed intra-cluster correlation coefficients in a cluster survey sample of patient encounters in general practice in Australia

Knox, SA Chondros, P

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Publisher:: BioMed Central Ltd.
Publication Type:: Journal Article
Citation:: BMC Medical Research Methodology, 2004, 4:30 pp. 1 - 8
Issue Date:: 2004-01

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Field	Value	Language
dc.contributor.author	Knox, SA	en_US
dc.contributor.author	Chondros, P	en_US
dc.date.issued	2004-01	en_US
dc.identifier.citation	BMC Medical Research Methodology, 2004, 4:30 pp. 1 - 8	en_US
dc.identifier.issn	1471-2288	en_US
dc.identifier.uri	http://hdl.handle.net/10453/9635
dc.description.abstract	Background Cluster sample study designs are cost effective, however cluster samples violate the simple random sample assumption of independence of observations. Failure to account for the intra-cluster correlation of observations when sampling through clusters may lead to an under-powered study. Researchers therefore need estimates of intra-cluster correlation for a range of outcomes to calculate sample size. We report intra-cluster correlation coefficients observed within a large-scale cross-sectional study of general practice in Australia, where the general practitioner (GP) was the primary sampling unit and the patient encounter was the unit of inference. Methods Each year the Bettering the Evaluation and Care of Health (BEACH) study recruits a random sample of approximately 1,000 GPs across Australia. Each GP completes details of 100 consecutive patient encounters. Intra-cluster correlation coefficients were estimated for patient demographics, morbidity managed and treatments received. Intra-cluster correlation coefficients were estimated for descriptive outcomes and for associations between outcomes and predictors and were compared across two independent samples of GPs drawn three years apart. Results Between April 1999 and March 2000, a random sample of 1,047 Australian general practitioners recorded details of 104,700 patient encounters. Intra-cluster correlation coefficients for patient demographics ranged from 0.055 for patient sex to 0.451 for language spoken at home. Intra-cluster correlations for morbidity variables ranged from 0.005 for the management of eye problems to 0.059 for management of psychological problems. Intra-cluster correlation for the association between two variables was smaller than the descriptive intra-cluster correlation of each variable. When compared with the April 2002 to March 2003 sample (1,008 GPs) the estimated intra-cluster correlation coefficients were found to be consistent across samples.	en_US
dc.publisher	BioMed Central Ltd.	en_US
dc.relation.ispartof	BMC Medical Research Methodology	en_US
dc.subject.classification	General & Internal Medicine	en_US
dc.title	Observed intra-cluster correlation coefficients in a cluster survey sample of patient encounters in general practice in Australia	en_US
dc.type	Journal Article
utslib.citation.volume	4:30	en_US
utslib.for	111799 Public Health and Health Services not elsewhere classified	en_US
utslib.for	1117 Public Health and Health Services	en_US
pubs.embargo.period	Not known	en_US
pubs.organisational-group	/University of Technology Sydney
pubs.organisational-group	/University of Technology Sydney/Faculty of Business
utslib.copyright.status	open_access
pubs.consider-herdc	false	en_US
pubs.volume	4:30	en_US

Abstract:

Background Cluster sample study designs are cost effective, however cluster samples violate the simple random sample assumption of independence of observations. Failure to account for the intra-cluster correlation of observations when sampling through clusters may lead to an under-powered study. Researchers therefore need estimates of intra-cluster correlation for a range of outcomes to calculate sample size. We report intra-cluster correlation coefficients observed within a large-scale cross-sectional study of general practice in Australia, where the general practitioner (GP) was the primary sampling unit and the patient encounter was the unit of inference. Methods Each year the Bettering the Evaluation and Care of Health (BEACH) study recruits a random sample of approximately 1,000 GPs across Australia. Each GP completes details of 100 consecutive patient encounters. Intra-cluster correlation coefficients were estimated for patient demographics, morbidity managed and treatments received. Intra-cluster correlation coefficients were estimated for descriptive outcomes and for associations between outcomes and predictors and were compared across two independent samples of GPs drawn three years apart. Results Between April 1999 and March 2000, a random sample of 1,047 Australian general practitioners recorded details of 104,700 patient encounters. Intra-cluster correlation coefficients for patient demographics ranged from 0.055 for patient sex to 0.451 for language spoken at home. Intra-cluster correlations for morbidity variables ranged from 0.005 for the management of eye problems to 0.059 for management of psychological problems. Intra-cluster correlation for the association between two variables was smaller than the descriptive intra-cluster correlation of each variable. When compared with the April 2002 to March 2003 sample (1,008 GPs) the estimated intra-cluster correlation coefficients were found to be consistent across samples.

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http://hdl.handle.net/10453/9635