Continuous ecotoxicological data evaluated relative to a control response

This article describes a generalized nonlinear regression method that models continuous ecotoxicological response data evaluated relative to a control response. The major improvement and difference from the methods described in the literature is consideration of the covariance between data, which is induced when modeling responses relative to a control response.

The capability to estimate ECp's (the concentration that corresponds to p% effect), such as EC10 and EC50, and their confidence limits is evaluated through a simulation study. The method is illustrated with real data from growth inhibition tests with freshwater microalgae. Recommendations are given on the choice of regression function, on how to handle initial stimulation and on test designs.