Nonparametric identification of the minimum effective dose

We consider identifying the minimum effective dose (MED) in a dose-response study, where the MED is defined to be the lowest dose level producing an e ffect over that of the zero-dose control. Proposed herein is a nonparametri c procedure based on the Mann-Whitney statistic incorporated with the step- down closed testing scheme. A numerical example demonstrates the feasibilit y of the proposed nonparametric procedure. Finally, the comparative results of a Monte Carlo level and power study for small sample sizes are presente d and discussed.