[R] cox models

Xiuyu Cong
Sun, 06 Nov 2005 16:13:27 -0000

Level 1 is treated as the "baseline". The coefficient for level 2 for
example is for the hazard ratio between level 2 and level 1. Same thing
for levels 3,4,5 in the output.

HTH,

On Sun, 6 Nov 2005, bertrand wrote:

> Hello,
> i'm a french student of medical oncology and i'm working on breast
> cancer. I have a variable with the histologic type of tumor wich is
> between 1 and 5. I use as.factor function to make some variable with
> level between 1 and 5. When i put it in the cox model i have only the
> level between 2 and 5. The level 1 doesn't appear. I think i have to
> change the number of level but i don't really know. Please can you help
> me?
>
>
> Class
> Levels: 1 2 3 4 5
> coxph(formula = Surv(delai.etat, etat) ~ class, data = igr1)
>
>
>           coef exp(coef) se(coef)     z       p
> class2 -0.093     0.911    0.245 -0.38 7.0e-01
> class3 -0.749     0.473    0.286 -2.62 8.9e-03
> class4 -0.600     0.549    0.343 -1.75 8.0e-02
> class5 -0.874     0.417    0.197 -4.44 8.9e-06
>
> Likelihood ratio test=24.9  on 4 df, p=5.28e-05  n=740 (1 observations
> deleted due to missing)
>
>
>
> Thanks for your help
>
>
> Bertrand
>
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