
Hi all,


I am trying to detect association between a covariate and a disease outcome using R. This covariate shows time-varying effect, I add a time-covariate interaction item to build Cox model as follows:
COX <- coxph(as.formula("Surv(TIME,outcome)~eGFR_BASE+eGFR_BASE:TIME"),ori.data);


                                              coef   exp(coef)   e(coef)        z   p
eGFR_BASE                 6.40     603.5133     0.3702    17.3   0
eGFR_BASE:TIME -3.41      0.0329     0.0772   -44.2   0


But the result seems very different from that got by SPSS: 


                                                    B            	SE    	Wald	    df    	Sig.	    Exp(B)
eGFR_BASE        	        -13.603	  .548	  616.007	   1	     .000    	.000  
T_COV_*eGFR_BASE	.860 	.115	  55.859  	1	  .000	        2.362   



so my questions are :
1, Is it correct to deal with time dependent covariate in Cox regression using R? if not, how to do it ?
2, How T_COV_ was calculated in SPSS, and is it the same with the survival time?


Many thanks.
GZ
 		 	   		  
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