Relative risk and excess rate models in exposure-response analysis.

The cumulative dose of an environmental exposure and age are usually correlated. It is shown that if an excess rate model is the true relationship, a relative risk model based on standardized mortality ratios (SMR) may show a biased and even contradictory dose-response relationship if the incidence rate in the reference population increases rapidly by age. The choice of model should be based on biological plausibility rather than on available software, and in many cases it may be reasonable to analyze the data both according to a relative and to an excess risk model as the prior knowledge rarely favors one of these models. In a review of a volume of this journal, there were eight cohort studies analyzing dose-response relationship by comparing SMRs without reporting or analyzing excess rates. Thus, there seems to be some lack of awareness of the possible bias in analyzing exposure-disease associations by SMRs.