Document Detail

Sample size estimation using repeated measurements on biomarkers as outcomes.
MedLine Citation:
PMID:  7913674     Owner:  NLM     Status:  MEDLINE    
The objectives of this paper are to (1) examine methods of using longitudinal data in designing comparative trials and calculating sample sizes or power and (2) show the effect of autocorrelation of repeated measures on the assessment of sample sizes. A statistical model with a simple regression structure for the mean trajectory of the longitudinal data and a two-parameter model for the correlations of within-individual observations given by corr(yt,yt+s) = gamma s theta is used. The methods are illustrated by considering a two-group trial and investigating the effect of different values of the correlation parameters, gamma and theta on the sample size. The results show that taking account of the autocorrelation structure of longitudinal data may lead to more efficient designs. Specifically, the stronger the autocorrelation is, the smaller the sample size that is required.
A J Kirby; N Galai; A Muñoz
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Controlled clinical trials     Volume:  15     ISSN:  0197-2456     ISO Abbreviation:  Control Clin Trials     Publication Date:  1994 Jun 
Date Detail:
Created Date:  1994-08-24     Completed Date:  1994-08-24     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  8006242     Medline TA:  Control Clin Trials     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  165-72     Citation Subset:  IM; X    
Department of Epidemiology, Johns Hopkins School of Hygiene and Public Health, Baltimore, Maryland.
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MeSH Terms
AIDS Vaccines / administration & dosage,  immunology
Acquired Immunodeficiency Syndrome / immunology,  prevention & control
Biological Markers / blood*
CD4-Positive T-Lymphocytes / immunology
HIV Seropositivity / immunology,  therapy
HIV-1 / immunology
Leukocyte Count
Longitudinal Studies
Randomized Controlled Trials as Topic / statistics & numerical data*
Sampling Studies*
Treatment Outcome
Grant Support
Reg. No./Substance:
0/AIDS Vaccines; 0/Biological Markers
Comment In:
Control Clin Trials. 1995 Dec;16(6):449-52   [PMID:  8720021 ]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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