[R] need help with understanding coxph encoding

[David Winsemius]

On Feb 7, 2012, at 9:11 PM, summer wrote:

> Hi, in coxph,
> coxph(Surv(time, status)~x,data=alm).
> How to encode x? For example, if x has two groups, the treatment  
> group and
> control group. if I encode them as  1 and 2. Is the HR results
> treatment/control? What if I encode them as 0 and 1. I am confused  
> with how
> survival package works for HR. What should I do to get a treatment/ 
> control
> HR?

The proper way would be to construct "x" is as a factor. Then you will  
not be implicitly telling the function that it is dealing with  a  
numeric value. (In this simple case it probably  doesn't really  
matter. The coefficient for the effect would be the same.

-- 

David Winsemius, MD
West Hartford, CT