Detecting hormesis using a non-parametric rank test

When a dose-response experiment is conducted, the enhanced responses can be observed at low doses. This phenomenon is often called hormesis. The enhan ced responses at low doses does not necessarily mean the existence of horme sis. It is important to conduct statistical analyses to determine whether a departure from monotonic relationships is significantly different from the chance occurrence. This paper introduces a non-parametric rank test to det ect hormesis. To illustrate the use of this method, we apply it to the data from a Whole Effluent Toxicity test. We demonstrate that the occurrence of hormesis can be statistically evaluated by using this non-parametric rank test.