Including an Interaction Term Between Two Independent Variables $X _ { 1 } \text { and } X _ { 2 } \text {, }$

Multiple Choice

Including an interaction term between two independent variables, $X _ { 1 } \text { and } X _ { 2 } \text {, }$ allows for the following, except that:

A) the interaction term lets the effect on Y of a change in $X _ { 1 }$ depend on the value of $X _ { 2 }$
B) the interaction term coefficient is the effect of a unit increase in $X _ { 1 }$ and $X _ { 2 }$ above and beyond the sum of the individual effects of a unit increase in the two variables alone.
C) the interaction term coefficient is the effect of a unit increase in $\sqrt { \left( X _ { 1 } \times X _ { 2 } \right) }$
D) the interaction term lets the effect on Y of a change in $X _ { 2 }$ depend on the value of $X _ { 1 }$