SAS Survival Analysis IV: Cox Model with Time-dependet Variable

libname asa_data 'C:\ASA_SAS';
* Time-dependent variable;
ods output parameterestimates = temp1;
proc phreg data = asa_data.uis;
model time*censor(0) = treat off_trt tot;
if time <= los then off_trt = 0;
else off_trt = 1;
tot = treat*off_trt;
run;
* Compared with the following code;
data temp2;
set asa_data.uis;
if time <= los then off_trt = 0;
else off_trt = 1;
tot = treat*off_trt;
run;
proc phreg data = temp2;
model time*censor(0) = treat off_trt tot;
run;