Hello all, I have a problem and would really appreciate your input. So here it is: Context: c-statistics from cox regression analysis Samples: 16,942 participants below age 75 years old Events (death): 1,116 Variables: idn, duration, age, sex, censory Syntax Syntax used is adapted from SAS Global Forum Paper (1): Liu L, Forman S, Barton B. Fitting Cox model using PROC PHREG and beyond in SAS. SAS Glob Forum [Internet]. 2009 [cited 2015 Aug 4]; Available from: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.176.1835&rep=rep1&type=pdf Sy Syntax: proc phreg data=Below75allsubjectiveobjective; id idn; model duration*censory(0)= age sex; output out=obs survival=surv; run; data evtset; set obs; if censory=1; rename idn=idn_j surv=y_j duration=x_j; keep idn surv duration; run; proc sql; create table allset as select idn_j, y_j, x_j, idn as idn_i, surv as y_i, duration as x_i from evtset, obs where idn_j<>idn; quit; data concord; set allset; if (x_i<x_j and y_i>y_j) or (x_i>x_j and y_i<y_j) then concord=1; else concord=0; run; data _null_; set concord end=eof; retain nch ndh; if _N_=1 then do; nch=0; ndh=0; end; if concord=1 then nch+1; if concord=0 then ndh+1; if eof=1 then do; call symput('ch',trim(left(nch))); call symput('dh',trim(left(ndh))); call symput('uspairs',trim(left(_n_))); end; run; data _null_; set Below75allsubjectiveobjective end=eof; if eof=1 then call symput('totobs',trim(left(_n_))); run; %put &ch &dh &uspairs &totobs; data calculat; ch=input("&ch",12.0); dh=input("&dh",12.0); uspairs=input("&uspairs",12.0); totobs=input("&totobs",10.0); pc=ch/(totobs*(totobs-1)); pd=dh/(totobs*(totobs-1)); c_hat=pc/(pc+pd); w=(2*1.96**2)/(totobs*(pc+pd)); low_ci_w=((w+2*c_hat)/(2*(1+w)))-(sqrt((w**2+4*w*c_hat*(1- c_hat))/(2*(1+w)))); upper_ci_w=((w+2*c_hat)/(2*(1+w)))+(sqrt((w**2+4*w*c_hat*(1- c_hat))/(2*(1+w)))); run; This syntax runs smoothly without any errors. Output when adding different covariates: Covariates Ch Dh Uspairs Totobs pc pd c_hat w low_ci_w upper_ci_w None 18752674 153482 18906156 16942 0.065 0.001 0.992 0.007 0.977 1.000 Sex 16284756 2621400 18906156 16942 0.057 0.009 0.861 0.007 0.818 0.899 Age, Sex 12821742 6084414 18906156 16942 0.045 0.021 0.678 0.007 0.622 0.732 C-hat from the output is the c-statistics calculated, is that correct? Problem: Why is C-statistics decreasing when adding more covariates? How do I interpret the c-statistics results? Thank you in advance
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