. 2020 Jan 16;17(2):572. doi: 10.3390/ijerph17020572

Table 2.

Types and strengths of interaction between two independent variables.

Types and Strengths of Interaction	Discriminant Basis
Weaken, nonlinear	$q (X 1 \cap X 2) < \min (q (X 1), q (X 2))$
Weaken, nonlinear, single	$\min (q (X 1), q (X 2)) < q (X 1 \cap X 2) < \max (q (X 1), q (X 2))$
Enhance, bi	$q (X 1 \cap X 2) > \max (q (X 1), q (X 2))$
Independent	$q (X 1 \cap X 2) = q (X 1) + q (X 2)$
Enhance, nonlinear	$q (X 1 \cap X 2) > q (X 1) + q (X 2)$