I am trying to analyze correlated data with PHREG. The clustering / grouping variable is drug class. What is the best way of getting accurate estimates?
OPTION A
proc phreg data = data covsandwich(aggregate);
class route (ref="0") drug_class / ref=first;
model follow_up_time*discontinued(0) = drug_age route / rl=both;
id drug_class;
run;
OPTION B
proc phreg data = data covsandwich(aggregate);
class route (ref="0") drug_class / ref=first;
model follow_up_time*discontinued(0) = drug_age route /rl=both;
strata drug_class;
run;
In other words what is the difference between strata and ID when trying to account for correlated data?
Thank you very much.
