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 EC_p'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.

Key Words
Covariance; Dose-Response Curves; Generalized Nonlinear Regression.

Jens Strodl Andersen is Ph.D. student, Helle Holst is Associate Professor of Statistics, and Henrik Spliid is Professor of Statistics, Department of Mathematical Modeling, IMM, Building 321, Technical University of Denmark, DK-2800 Lyngby, Denmark (E-mail: jsa@imm.dtu.dk). Helle Andersen is Ph.D. student, Medical System, Statistical Department, Novo Nordisk A/S, 3400 Hillerød, Denmark. Anders Baun is a Ph.D. student, and Niels Nyholm is Associate Professor, Department of Environmental Science and Engineering, Technical University of Denmark, DK-2800, Lyngby, Denmark.