[R] search tutorial for function "tt" in cox.zph

[johann.delcourt at ulg.ac.be]

Hye,

I am writing to request your help. 

I am working on survival curve analysis with Cox model (cox.zph). After to test the proportionality condition for each covariant (independence to the time), the time effect is very significant and I must adapt my model, by the addition of a function dependent on the time for each time-dependent covoriant. My problem is I don’t know how determine this function. It seems there is a function “tt” in R which can help to find this function and integrate it in my Cox model.

I am searching a good tutorial (or book reference) with example(s) to understand and apply the function “tt” in R;

Thanks in advance

Johann Delcourt