> 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.harr...@vanderbilt.edu] Sent: 25 February 2009 17:50 To: Eleni Rapsomaniki Cc: r-help@r-project.org Subject: Re: [R] C-index for models fitted using start, stop in Surv? 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 ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
