Thanks very much for that - your notes have been extremely helpful and
answered my question fully! However, I have found that when
introducing these 'interaction effects between continuous variables',
if I include the slope term *or* the intercept term the coefficients
are significant, but when including both (as you suggest), the
coefficients are insignificant. Does the intercept term need to be
included where the mid-point of the variable that is being added in is
zero, as in this case?
Best regards,
Robert Gaskell
I'm not quite sure what you are doing - by "intercept" do you mean the
dummy variable for group membership? Or, do you literally mean that you
have specified -noconstant- when running your models? Anyway, whatever you
mean, my guess is you want it (constant and/or dummy variable) in there.
