Time varying covariate is polytomous for cox proportional regression, how to deal and interpret?

SAS-questioner — Fri, 20 May 2022 21:17:33 GMT

I am trying to conduct a cox proportional hazard, after I checked the assumptions, it turns out that interaction exists. So, I have to put an interaction into the model. But the time varying covariate is polytomous variable with four categories. I used the below code to run analysis:

proc phreg data=one;
	class treatment(ref='1');
	model time*survival(0) = treatment treat_ti;
	treat_ti=treatment*time;
run;

The treatment is time varying covariate with four categories. And I get the results like this:

                                       Parameter      Standard                  Hazard
 Parameter      DF      Estimate         Error    Chi-Square    Pr > ChiSq       Ratio    

 treatment 2     1      -0.33139       0.02126     1183.5006        <.0001   0.386    
 treatment 3     1      -0.17445       0.02588       45.4387        <.0001   0.745    
 treatment 4     1      -0.69876       0.03591      278.0054        <.0001   0.646    
 treat_ti        1      0.01096     0.0001625      145.9549         <.0001   1.023

I am not sure if I put the interaction term wrong because the treatment is 4-category variable, but there is only one interaction term which makes the interpretation really hard. When I saw the K-M plot, only two treatments had the interaction. So my question is, did I do it correctly? If I did it correctly, how to interpret these results? Could anyone help me with it? Thank you!

topic Time varying covariate is polytomous for cox proportional regression, how to deal and interpret? in Statistical Procedures

Time varying covariate is polytomous for cox proportional regression, how to deal and interpret?