Hello dear form members,
Please consider the following regression model:
y = a + b1x1 + b2x1^2 + b3x2 + b4x1*x2 + e,
Note that x1 is (1) used as a moderator, therefore both main effect (b1x1) and interaction (b4x1*x2) are included; and (2) also included as a squared term (b2x1^2) to test for curvilinearity.
I understand that the effect of x2 is interpreted as “conditional” effect at the mean value of x1 — no problem here.
But what about the squared term -- how shall I interpret the b2 coefficient in the presence of interaction?
Thank you in advance!
Please consider the following regression model:
y = a + b1x1 + b2x1^2 + b3x2 + b4x1*x2 + e,
Note that x1 is (1) used as a moderator, therefore both main effect (b1x1) and interaction (b4x1*x2) are included; and (2) also included as a squared term (b2x1^2) to test for curvilinearity.
I understand that the effect of x2 is interpreted as “conditional” effect at the mean value of x1 — no problem here.
But what about the squared term -- how shall I interpret the b2 coefficient in the presence of interaction?
Thank you in advance!