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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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I am going to pull a Ksharp trick here and ask someone else who knows quite a bit about PHREG. So calling @FreelanceReinh
SteveDenham
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Thanks, Steve. Sadly, I have never dealt with the case of non-proportional hazards. By a quick web search I found two conference papers on this particular subject:
[1] suggests an "interaction of particular covariate with a function of time variable" (which might be what the OP is trying to implement) or, alternatively, a "stratification model."
[2] uses a Bayesian approach.
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Thank you both very much for your help! I really appreciate it.