The importance of specifying the underlying biologic model in estimating the probability of causation

There are a number of contexts in which interested parties wish to estimate the probability that an individual's injury was caused by radiation or a toxic chemical. It has been shown, however, that such calculations cannot be made based on epidemiologic data alone, without assumption of a biologic model for the disease process and without a specific definition of causation. To illustrate the relevant theorems, we present a number of examples in which different biologic models produce different values for the probability of causation for individuals from the same population-based epidemiologic data and dose-response curves. As a result of these ambiguities, it is important that anyone attempting to calculate probability of causation for individuals explicitly state the biologic model that has been assumed, as well as state the definition of causation being used. The analyst should test the robustness of the calculations by repeating them for a broad range of underlying biologic models.