A ratio-to-control Williams-type test for trend
Article first published online: 11 OCT 2010
Copyright © 2010 John Wiley & Sons, Ltd.
Volume 10, Issue 4, pages 289–292, July/August 2011
How to Cite
Hothorn, L. A. and Djira, G. D. (2011), A ratio-to-control Williams-type test for trend. Pharmaceut. Statist., 10: 289–292. doi: 10.1002/pst.464
- Issue published online: 25 JUL 2011
- Article first published online: 11 OCT 2010
- multiple comparison;
- Williams trend test
Under certain conditions, many multiple contrast tests based on the difference of treatment means can also be conveniently expressed in terms of ratios. In this paper, a Williams test for trend is defined as ratios-to-control for ease of interpretation and to obtain directly comparable confidence intervals. Simultaneous confidence intervals for percentages are particularly helpful for interpretations in the case of multiple endpoints. Methods for constructing simultaneous confidence intervals are discussed under both homogeneous and heterogeneous error variances. This approach is available in the R extension package mratios. The proposed method is used to test for trend in an immunotoxicity study with several endpoints as an example. Copyright © 2010 John Wiley & Sons, Ltd.