SYNERGISM, ATTRIBUTABLE RISK AND INTERACTION FOR 2 BINARY EXPOSURE FACTORS

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