Hello, I have a question about proc phreg with multiple groups and violated PH ratio. I would like to compare the re-intervention on patients who had a procedure. There are three procedures (Group=0,1,2) and the outcome is reintervention (0 ,1). Comparison of interest is 1) Group 1 vs 0 and 2) Group 1 vs 2. Proportional hazard ratio is violated, so I would like to include interaction term to evaluate hazard ratio at each time point (5, 10, 15 years after procedure). I created two dichotomous variables to express Group. Group 0: A=0, B=0, Group 1: A=1, B=0, Group 2: A=0, B=1. I think contrast statement should be used, but I am not quite sure what interaction term is included. proc phreg data=X; model Time_to_reintervention*reintervention(0)=A B interaction/rl ; interaction=??; contrast 'time=5' A ? B ? interaction ? / estimate=exp e; contrast 'time=10' A ? B ? interaction ? / estimate=exp e; contrast 'time=15' A ? B ? interaction ? / estimate=exp e; run; I would greatly appreciate if if you could help... Thank you very much.
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