Non-linearity and Statistics - Implications of Hormesis on Dose-response Analysis

In medical applications of statistics, such as drug testing or risk assessment, most investigators usually expects linear dose-response pattern and is rather surprised finding that the effects on some individuals are even opposite than those expected from the assumption of linearity. We provide several examples of the non-linear doseresponse pattern, the phenomenon called hormesis, both chemical and radiation hormesis. We also discuss possible explanation of hormesis based on cybernetic regulation mechanism or on chaotic attractor hypothesis, as well as consequences of hormesis for epidemiology and medical statistics.