Categorical variables and interaction in MLR

noetsi

Fortran must die
#2
It depends on whether your theory supports doing so or not. Dummy variable interaction is not different than any other interaction.
 

spunky

Doesn't actually exist
#5
but as Jake corrected in a post of mine sometime earlier, the interpretation of dummy-coded interactions can be pretty confusing. effects coding is what i think people usually go for when they're dealing with interactions between categorical variables...
 

Dason

Ambassador to the humans
#6
Is effects coding the {-1, 1} way of coding things?

Edit: And by that I mean it's either 0 or 1 for all groups except one group that is -1 for all of the dummy variables...
 

Dason

Ambassador to the humans
#8
Meh - I don't really use that very often. But if I think about it when I learned it I think it was "factor effects coding" - so... yeah ... I guess effects coding makes sense.
 

noetsi

Fortran must die
#9
Strange I always use reference coding...although the only thing I usually care about an interaction variable is if its sig or not. When it is I try to find out why it is substantively and look at graphs and run the regression at different levels of the interacting variables...

I am not sure what it matters if you use reference or effect coding if your doing that :)