Hello~ I want to explore the change in cognitive decline associated with air pollution exposure. I have two measurements of cognitive score (continuous variable) and multiple measurements of PM (continuous variable). My SAS code is as following: proc glimmix empirical ; class id; model cognitive_score=PM year_air PM*year_air / dist=normal link=identity solution; random intercept / subject=id; run; The individual effect of PM and year_air on cognitive change is significantly negative, but the effect of interaction term on cognitive change is significantly negative. How I explain the interaction term? Should I plot the related plot to explain? In addition, I found the intercept and the estimate of PM are too strange and too large when I put the variable of time (year_air) in the model. Why is it? Did anyone can help me? Thank you.
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