[R] C-index for models fitted using start, stop in Surv?

[Frank E Harrell Jr]

Eleni Rapsomaniki wrote:
> Dear R-users,
> 
> One can use the rcorr.cens function in Design to compute the C index when only the stop time is indicated (I think implicitely start=0 in that case). When the start and stop times are used in a Surv object, e.g. 
> 
> library(Design)
> S=with(heart, Surv(start,stop,event))
> 
> the object returned is no longer a single number vector, so none of the following ways to compare a model fit to S makes sense:
> 
> rcorr.cens(-cph(S~ age+transplant+surgery, heart)$linear.predictors, with(heart, Surv(start,stop,event)))
> #       C Index            Dxy           S.D.              n        missing 
> #      4.95e-01      -9.66e-03       7.15e-02       1.72e+02       0.00e+00 
> #this seems bad because it compares the fit to a different Surv than the one used to fit it (S, above)
> 
> rcorr.cens(-cph(S~ age+transplant+surgery, heart)$linear.predictors, with(heart, Surv(stop-start,event)))
> #       C Index            Dxy           S.D.              n        missing 
> #      6.02e-01       2.03e-01       7.54e-02       1.72e+02       0.00e+00 
> 
> Is there some way I can compute the correlation for this type of survival time specification in R? If not, does anybody have some tips on how to go about computing it myself?
> 
> Many Thanks
> 
> Eleni Rapsomaniki
> Research Associate
> Strangeways Research Laboratory
> Department of Public Health and Primary Care
> University of Cambridge
>  
> 

rcorr.cens is not meant for that.
Frank

-- 
Frank E Harrell Jr   Professor and Chair           School of Medicine
                      Department of Biostatistics   Vanderbilt University