Re: [R] Nagelkerkes R2N

2009-07-15 Thread North, Bernard V
I am interested Andrea is whether you ever established why your R2 was 1. I have had a similar situation previously. My main issue though, which I'd be v grateful for advice on, is why I am obtaining such negative values -0.3 for Somers Dxy using validate.cph from the Design package given m

[R] negative Somers D from Design package

2009-07-15 Thread North, Bernard V
Dear R help My problem is very similar to the analysis detailed here. If we use the mayo dataset provided with the survivalROC package the estimate for Somer's Dxy is very negative -0.56. The Nagelkerke R2 is positive though 0.32. I know there is a difference between explained variation and predi

[R] using axis.Date with interaction.plot

2009-10-13 Thread North, Bernard V
Dear List I want to plot multiple time series (several outcomes) with dates at intervals on the x axis and a legend. Is it possible to use axis.Date to get dates, at intervals in my case, on the x axis of a (multiple) time series plot. The axis.Date in the code below doesn't produce any dates

[R] output (p-values) of "fastbw" in Design package

2009-10-27 Thread North, Bernard V
I am using the validate option in the Design package with the Cox survival model. I am using the bw=T option which, like the fastbw function, performs a backward elimination variable selection The output includes a series of columns (below) giving information on eliminated variables. My question

[R] confidence intervals for Harrell's c-index in survival setting

2010-08-17 Thread North, Bernard V
Dear All, Is it possible to get confidence intervals for Harrell's concordance index or, equivalently, Somer's D using the rms package or in some other way ? I have survival data it would be the c-index in the Cox model setting Many thanks Dr Bernard North Statistical Consultant Statistical

[R] C-statistics (AUCs) from rcorr.cens or survcomp time-dependent ROC curves

2011-03-25 Thread North, Bernard V
I am using the rcorr.cens function from the Hmisc package and the time-dependent ROC curve obtained using tdrocc in the survcomp package. I understand that the C statistic from rcorr.cens has to be subtracted from 1 if high values of the risk variable lower survival. Given that I wonder what the

[R] relation between tdrocc AUC and c-statistic from rcorr.cens

2011-06-21 Thread North, Bernard V
I am using the rcorr.cens function from the Hmisc package and the time-dependent ROC curve obtained using tdrocc in the survcomp package. I understand that the C statistic from rcorr.cens has to be subtracted from 1 if high values of the risk variable lower survival. Given that I wonder what the