Synergism, attributable risk and interaction for two binary exposure factors

Abstract

SUMMARY The concept of attributable risk for one binary exposure factor is reviewed and then extended to two factors. Synergistic, parallel and two other kinds of joint action between the two factors are defined, and it is shown how to estimate the amounts of action of each kind. A proposal of Hamilton (1979) is reviewed. The additive and multiplicative models of no interaction are freshly interpreted in terms of synergistic and parallel action.