Document Detail

Calculation of power and sample size with bounded outcome scores.
MedLine Citation:
PMID:  8341866     Owner:  NLM     Status:  MEDLINE    
The two-sample Wilcoxon rank sum test is the most popular non-parametric test for the comparison of two samples when the underlying distributions are not normal. Although the underlying distributions need not be known in detail to calculate the null distribution of the test statistic, parametric assumptions are often made to determine the power of the test or the sample size. We encountered difficulties with this approach in the planning of a recent clinical trial in stroke patients. It is shown that, for power and sample size estimation, it can be dangerous to apply the classical formulae routinely, especially with outcome scores having a U-shaped or a J-shaped distribution. As an example we have taken the Barthel index, a quality-of-life outcome measure in stroke patients. Further, we have investigated alternative methods by means of Monte Carlo simulation. The distributional characteristics of the estimated powers were compared. Our findings suggest more appropriate computer software is necessary for the calculation of power and sample size when efficacy is measured by a non-parametric method.
E Lesaffre; I Scheys; J Fröhlich; E Bluhmki
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Publication Detail:
Type:  Clinical Trial; Comparative Study; Journal Article; Randomized Controlled Trial    
Journal Detail:
Title:  Statistics in medicine     Volume:  12     ISSN:  0277-6715     ISO Abbreviation:  Stat Med     Publication Date:  1993 Jun 
Date Detail:
Created Date:  1993-09-02     Completed Date:  1993-09-02     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  8215016     Medline TA:  Stat Med     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  1063-78     Citation Subset:  IM    
Department of Epidemiology, Catholic University Leuven, Belgium.
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MeSH Terms
Cerebrovascular Disorders / drug therapy,  epidemiology
Clinical Trials as Topic / methods*
Double-Blind Method
Monte Carlo Method
Sampling Studies*
Tissue Plasminogen Activator / therapeutic use
Reg. No./Substance:
EC Plasminogen Activator

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

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