There are 3 groups. And I want to get the hazard ratio for group 1 vs group 3, and group 2 vs group 3. The results that are generated from below 2 methods are not the same. So should I better put all 3 groups into PHREG, and set group 3 as reference level, Or should I select 2 groups each time when I execute PHREG procedure ? Thank you very much.   Method 1:  proc phreg data = xx alpha=0.05;     class trt (ref="3");     model aval*cnsr(1)=trt /ties=exact;     hazardratio trt / diff=all; run; Method 2:  proc phreg data = xx(where=(trt in (1,3) )) alpha=0.05;     class trt (ref="3");     model aval*cnsr(1)=trt /ties=exact;     hazardratio trt ; run; proc phreg data = xx(where=(trt in (2,3) )) alpha=0.05;     class trt (ref="3");     model aval*cnsr(1)=trt /ties=exact;     hazardratio trt ; run; ... View more