adding interaction terms error
Hey! I'm wondering if you could please help me?
I'm trying to add an interaction term into the glmsmurf model, and I'm getting the following error: "No unused levels can be present in the predictor 'inter.user_age.EngineVolume'. Please remove the unused factor levels." I have defined both predictors separately before including the interaction term, and I'm not aware of any unused levels (I've checked dropping unused levels using the droplevels function but nothing changed). How could I go about fixing this error?
Thank you and apologies if I've missed something trivial here, I'm still a beginner in R!