129 Interaction terms the general formula

In this video, we introduce the “master formula” for interaction models in econometrics, showing how relationships between variables can depend on one another. Starting from the general model y = β0 + β1x + β2z + β3xz + u, we explain how the interaction term xz allows the effect of one variable to vary with the level of another. By deriving the partial effects, we show that the impact of x on y becomes β1 + β3z, and similarly, the effect of z on y depends on x, highlighting the two-way nature of interactions. We interpret β3 as the key “slope change” parameter and build intuition for how interaction models capture more flexible, real-world relationships. This foundational framework sets the stage for understanding all common cases of interaction models, including dummy–dummy, dummy–continuous, and continuous–continuous interactions. Visit AxiomTutoring.com and subscribe to @AxiomTutoringCourses.