I am using SAS for linear mixed modeling in my dataset. The model also consists of three covariates. During the modeling process, I am also checking on whether there is an interaction between covariates and a group variable (one of the other fixed effect variables). For this, I included three interaction terms in the model between three covariates and the group variable. However, the addition of interaction terms inflates the denominator degree of freedom more than what is expected. Without interaction terms, the denominator degrees of freedom look fine. Any thoughts or suggestions on this?
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