Dose-response models: how might we think about linearity and nonlinearity?

We add to the issues raised by Dr David Ropeik's article Risk Communication and Non-Linearity (forthcoming, BELLE Newsletter, 2008) regarding the thinking about the acceptance of linear and nonlinear (hormetic) dose-response models. We summarize some of the perceptual aspects discussed by Ropeik (2008) and comment on decision-making by the single decision-maker. It seems that the heuristics discussed by Ropeik (2008) are related to those private decision-makers who may not benefit from extensive technical, scientific, and legal advice sufficiently to make well-informed decisions and, perhaps more importantly, may not have the funds for that advice. Dose-response models are intangible, abstract quantities: unlike private goods and services, they are not priced by the market. We suggest a duality between the private and the public decision-maker that in the end may loose its crispness, because it can occur in the same person. Nonetheless, this duality is evident at the analysis phase of decision-making, relative to the decision phase, and thus, provides a convenient way to address the issues addressed by Ropeik (2008). In particular, for at least legal and common sense reasons, the public decision-maker must follow a scientific-analytical causal process - as represented by models of dose-response - to select and justify her choice of one over the other. Whether the final decision as to which model is to be used in regulatory law is a matter that goes beyond the analytical aspects of the choice and is governed by political and other aspects of governance.