Dear SAS users,
I would like to ask a question on the PHREG procedure. In my question, I will use an open dataset on bladder cancer (attached), where patients got recurrent events of cancer, and time from entry to the study to each of the cancers is known.
I apply marginal type of multiple events models to these data, that is, in the PHREG, I stratify the model by events type (enum variable). As usual for these type of models, I use robust variance estimation by adding ID statement (correlation within patient id).
proc phreg data=survival.bladder2 covs(aggregate);
model futime*status(0)=rx size number / ties=efron;
strata enum;
id id;
run;
With that code, the PHREG procedure provides an overall hazard ratio for treatment groups, but I would like to know how treatment affects the hazard of each of the events. I understand that I simply need to add an interaction term between rx (treatment) and enum (event type), but not sure how to do that. I tried just add rx*enum in the MODEL statement, but that isn’t correct (enum was treated as numerical, I think).
Would anyone be so kind to share how they would add a treatment by event interaction in this PHREG procedure?
Thank you!
Marina
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