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A ratio-to-control Williams-type test for trend.
Ludwig A Hothorn1, Gemechis D Djira
1Institute of Biostatistics, Leibniz University of Hannover, Hannover, Germany. hothorn@biostat.uni-hannover.de
Pharmaceutical Statistics
|October 12, 2010
Summary
This study introduces a ratios-to-control Williams test for trend analysis, simplifying interpretation and enabling direct comparison of confidence intervals for multiple endpoints. The method is particularly useful for analyzing immunotoxicity studies with various outcomes.
Area of Science:
- Biostatistics
- Statistical Methods
- Toxicology
Background:
- Multiple contrast tests often rely on treatment mean differences.
- Expressing these tests as ratios offers potential for enhanced interpretation and comparable confidence intervals.
Purpose of the Study:
- To define a Williams test for trend using ratios-to-control.
- To develop methods for constructing simultaneous confidence intervals for percentages, especially for multiple endpoints.
- To provide a practical tool for trend analysis in toxicological studies.
Main Methods:
- Defining a Williams test based on ratios-to-control.
- Discussing methods for simultaneous confidence intervals construction under homogeneous and heterogeneous error variances.
- Utilizing the R extension package 'mratio' for implementation.
Main Results:
- The ratios-to-control approach facilitates direct comparison of confidence intervals.
- Simultaneous confidence intervals for percentages are effective for multiple endpoint interpretation.
- The proposed method was successfully applied to an immunotoxicity study.
Conclusions:
- The ratios-to-control Williams test offers a valuable alternative for trend analysis.
- This method enhances interpretability and comparability of results, particularly in complex studies.
- The 'mratio' package provides accessible implementation for these statistical techniques.
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