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

rcorr.cens is not meant for that.

Thank you for the clarification. On a second thought, I think (hope) a
time-dependent AUC index should be more appropriate in this case, such
as survivalROC. 

Many many thanks for all your help!

Eleni Rapsomaniki
 
Research Associate
Tel:     +44 (0) 1223 740273
Strangeways Research Laboratory
Department of Public Health and Primary Care
University of Cambridge
 

-----Original Message-----
From: Frank E Harrell Jr [mailto:f.harrell at vanderbilt.edu] 
Sent: 25 February 2009 17:50
To: Eleni Rapsomaniki
Cc: r-help at r-project.org
Subject: Re: [R] C-index for models fitted using start, stop in Surv?

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