adding interaction terms in logistic regression

I'm trying to add an interaction term to a logistic regression in SPSS and am having some trouble.

Basically, my data is all categorical. My design is set up that for a wildlife project, I had two types of bait (one treatment, one control) and several different types of bait that I treated to see if I could make bears stop eating the treatment bait. I had two time periods (pre-treatment and treatment) where I recorded if the bear ate both baits. So my predictors are bait type, time and protocol. I need to test the interactions before the main effects, but I can't seem to figure out how to do this using the help menus, and am basically stuck!

Hoping some one can help me with this...


New Member
You can create a new variable out of an old one and then give it the mathematical formula you want for the interaction term e.g. treatment X bait and then include that into the model. but the interpretation is going to be hard.....