Friday, November 21, 2008
Betas for interaction model
After adding the interaction term to the second model, it seems unnesscessary to explain the betas for the gender and PAQ variables because they have already been explained through the interaction term interpretation. Is it then necessary to interpret the Betas for gender and PAQ for the second model in the write up after you have already explained the interaction term?
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I believe that the answer is "no." As your interaction is the first most important effect that you must describe before you can describe any main effects, the betas for gender and PAQ (as main effects) reflect the presence of an interaction between the two. You must simply describe what the main effect means in the presence of the interaction which is what you are indicating in having explained these betas through the interaction term.
I don't think you're saying this, but just to make sure, the inclusion of the interaction in model two should show a difference in your variance for your predictors between model one and two (that is if there is any effect of the interaction). Therefore, it is important to make sure that the main effect of the variable is described in your second model, the explanation of which will only make sense in respect to the presence of an interaction effect.
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