Fig. 1.

Additivitiy and multiplicativity along a continuum.

Note: ${\mu }_{11}^A$ is the additive prediction of a statistical interaction between two risk factors and ${\mu }_{11}^M$ it the multiplicative prediction. Sub-multiplicativity and super-multiplicativity are mutually exclusive concepts, as are sub-additivity and super-additivity. Strictly multiplicative and super-multiplicative relationships necessarily implies super-additivity. Sub-multiplicativity and all three types of additivity (super-, strictly-, and sub-additivity) may co-exist.