Once interaction has been established between $x _ { 1 }$ and $x _ { 2 }$, the first-order terms for $x _ { 1 }$ and $x _ { 2 }$ may be deleted from the regression model leaving the higher-order term containing the product of $x 1$ and $x _ { 2 }$.

Question

Quizplus · Accepted Answer

The first-order terms for $x_1$ and $x_2$ should not be deleted from the regression model when an interaction term is included because the main effects (first-order terms) of $x_1$ and $x_2$ are still important for interpreting the independent effect of each variable on the outcome, aside from their interaction.

Once Interaction Has Been Established Between x1x _ { 1 }x1​

Once Interaction Has Been Established Between $x _ { 1 }$