Table 1 Types of interaction between two covariates.
From: Heterogeneity and the determinants of PM2.5 in the Yangtze River Economic Belt
Diagram | Criterion | Interaction |
|---|---|---|
| q(X1 ∩ X2) < Min(q(X1), q(X2)) | Nonlinear weakening |
| Min(q(X1), q(X2)) < q(X1 ∩ X2) < Max(q(X1), q(X2)) | Univariate nonlinear weakening |
| q(X1 ∩ X2) > Max(q(X1), q(X2)) | Bivariate enhancement |
| q(X1 ∩ X2) = q(X1) + q(X2) | Independent |
| q(X1 ∩ X2) > q(X1) + q(X2) | Nonlinear enhancement |
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Min(q(X1), q(X2)) is the minimum value between q(X1) and q(X2); 
Max(q(X1), q(X2)) is the maximum value between q(X1) and q(X2); 
q(X1) + q(X2) is the sum of q(X1) and q(X2); 
q(X1 ∩ X2) is the interaction between q(X1) and q(X2).
Min(q(X1), q(X2)) is the minimum value between q(X1) and q(X2); 
Max(q(X1), q(X2)) is the maximum value between q(X1) and q(X2); 
q(X1) + q(X2) is the sum of q(X1) and q(X2); 
q(X1 ∩ X2) is the interaction between q(X1) and q(X2).