Hi everyone, I am trying to get hazard ratios and wald chi-square tests for the comparison of each experimental arm vs. control. We have two experimental treatments and one control group with randomization 1:1:1; i_adtte is a time-to event ADAM dataset TRTPN is numeric "treatment arm" 1='A' 2='B' 3='Control' (Ref) AVAL is the time to event. CNSR controls censoring There are no missing values for any of the cases in the three arms. I wonder why I get different for HRs, confidence limits and chi-square tests when I apply two contrast statements on the three-arm data (A) or when I select the data for each comparison and then apply a single contrast (B1) / (B2). How do the data from the arm not included in a contrast (For example arm B) intervene in the calculation of the main effect of the other arm (For example arm A) against the control group? What should be the correct approach (separate or joint contrasts)? Many Thanks in advance. JG (A) proc phreg data = i_adtte; class TRTPN (ref=LAST)/ param = ref; model AVAL*CNSR(1) = TRTPN; hazardratio TRTPN ; contrast 'A vs. Control' TRTPN 1 0; contrast 'B vs. Control' TRTPN 0 1; run; (B1) proc phreg data = i_adtte; where trtpn in (1 3); class TRTPN (ref=LAST) / param = ref; model AVAL*CNSR(1) = TRTPN; hazardratio TRTPN; contrast 'A vs. Control' TRTPN 1 0 ; run; (B2) proc phreg data = i_adtte; where trtpn in (2 3); class TRTPN (ref=LAST)/ param = ref; model AVAL*CNSR(1) = TRTPN; hazardratio TRTPN; contrast 'B vs. Control' TRTPN 1 0 ; run;
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