Simultaneous Confidence Intervals for Ratios with Applications to the Comparison of Several Treatments with a Control

G. Dilba; F. Bretz; V. Guiard; L. A. Hothorn

doi:10.1055/s-0038-1633899

Methods of Information in Medicine, Table of Contents

Methods Inf Med 2004; 43(05): 465-469
DOI: 10.1055/s-0038-1633899

Original Article

Schattauer GmbH

Simultaneous Confidence Intervals for Ratios with Applications to the Comparison of Several Treatments with a Control

G. Dilba

¹Bioinformatics Unit, University of Hannover, Hannover, Germany

,

F. Bretz

²Novartis Pharma AG, Basel, Switzerland

,

V. Guiard

³Research Unit Genetics and Biometry, Research Institute for the Biology of Farm Animals, Dummerstorf, Germany

,

L. A. Hothorn

¹Bioinformatics Unit, University of Hannover, Hannover, Germany

› Author Affiliations

Abstract

Summary

Objectives: In this article, we illustrate and compare exact simultaneous confidence sets with various approximate simultaneous confidence intervals for multiple ratios as applied to many-to-one comparisons. Quite different datasets are analyzed to clarify the points.

Methods: The methods are based on existing probability inequalities (e.g., Bonferroni, Slepian and Šidàk), estimation of nuisance parameters and re-sampling techniques. Exact simultaneous confidence sets based on the multivariate t-distribution are constructed and compared with approximate simultaneous confidence intervals.

Results: It is found that the coverage probabilities associated with the various methods of constructing simultaneous confidence intervals (for ratios) in many-to-one comparisons depend on the ratios of the coefficient of variation for the mean of the control group to the coefficient of variation for the mean of the treatments. If the ratios of the coefficients of variations are less than one, the Bonferroni corrected Fieller confidence intervals have almost the same coverage probability as the exact simultaneous confidence sets. Otherwise, the use of Bonferroni intervals leads to conservative results.

Conclusions: When the ratio of the coefficient of variation for the mean of the control group to the coefficient of variation for the mean of the treatments are greater than one (e.g., in balanced designs with increasing effects), the Bonferroni simultaneous confidence intervals are too conservative. Therefore, we recommend not using Bonferroni for this kind of data. On the other hand, the plug-in method maintains the intended confidence coefficient quite satisfactorily; therefore, it can serve as the best alternative in any case.

Keywords

Bonferroni - Fieller’s theorem - many-to-one comparisons - multivariate t-distribution - simultaneous confidence sets

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References

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