18.4 Types of Interactions

1. Continuous by Continuous: Both $X$ and $M$ are continuous (e.g., age moderating the effect of income on spending).
2. Continuous by Categorical: $X$ is continuous, and $M$ is categorical (e.g., gender moderating the effect of education on salary).
3. Categorical by Categorical: Both $X$ and $M$ are categorical (e.g., the effect of a training program on performance, moderated by job role).