trying again...

I would really like some advice on the proper construction and interpretation of a small experiment and analysis using Logistic Regression. I had a sample of 50 people evaluate three different products (X1) and generate a score (X2). Then they indicated how likely they would be to purchase the product (DV - binary). Now, I want to model the relationship between X1, X2 and the DV. I'm running into difficulty setting up the model - I've read lots of forum posts about the use of interaction terms, but I cannot find a clear enough answer on the topic. Take the following model:

DV = Const. + X1 + X1*X2

X1 = product (categorical)

X2 = Centered Product score (continuous)

[assume all effects are significant at p < .000]

What's the problem with this model? if any? I've read some discussions which say this is fine, and other discussions that say you must have the main effect of X2 present in the model. Given inclusion of X2 as a main effect, what is the interpretation? Especially in the presence of the interaction term. ... my brain is stuck.

If anyone can help with a very clear explanation of what's happening in the model, I would really appreciate it.

Thank you kindly,

Ryan