Step-down trend tests for identifying the minimum effective dose.

Abstract

Many authors, most recently Tamhane, Hochberg, and Dunnett (18), have studied the problem of determining the minimum effective dose in dose-response studies. Based on past research and on findings from their own extensive simulation study, which covered a wide range of balanced normal homoscedastic situations, Tamhane et al. recommended a procedure they called SD2L, since it exhibited good performance in almost all the situations they studied. This method is a step-down procedure with a simple linear contrast-based trend test at each step. In this paper, we demonstrate that replacing the linear contrast trend test by Bartholomew's test leads to a procedure, SD2B, that consistently outperforms SD2L. In addition to the balanced normal homoscedastic framework, the finite sample performance of these procedures is also explored under unbalanced and/or heteroscedastic conditions. A third procedure, SD2W, which replaces the linear contrast test by Welch's test, offers some improvement over SD2B in a few heteroscedastic situations. In many cases, the increase in efficiency of SD2B and SD2W over SD2L exceeds 10%.