I have a research experiment to analyze where I would like to know if there is an interaction between two experimental factors. Let's say that the experiment has 4 replications (rep) and 4 treatments (trt) and I will call the measured variable xyz. I use the following language: proc glm; class rep trt; model xyz=rep|trt; run; The output will return dots in place of where p-values usually are. If I remove the interaction term from the model statement, I can get a p-value for rep and trt. Why does SAS not return p-values with more terms in the model? Is it a degrees of freedom issue?
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