is a covariate included in a model? does it hurt to exclude an interaction in a model when an interaction is excluded in a research model, why is it not included in the model? why don't we include interactions in a model why not include interaction in a model what is the difference between anabova and the naco model why are interactions not included in a model? why not include interaction in model how to include interactions in model why is it acceptable to not include interaction in model why not include interaction in model why not include interaction in model are interaction models acceptable when to not include interactions in the model can a covariate be included in models are interactional models of an experiment or of interest can an ancovva interaction be included why not include interactions in model? why not include interaction in a model when is it acceptable not to include interactions