Many thanks Eik. That was really helpful. I have found ROC function Epi package draws ROC curve for a combination of markers. What I tried was library(Epi) x <- rnorm( 100 ) z <- rnorm( 100 ) w <- rnorm( 100 ) tigol <- function( x ) 1 - ( 1 + exp( x ) )^(-1) y1 <- rbinom( 100, 1, tigol( 0.3 + 3*x + 5*z + 7*w ) ) out=ROC( form = y1 ~ x + z, plot="ROC",MI=FALSE) But this function does not produce SE or CI of the AUC or any other statistics. Any suggestion to get these? Thanks again Rasanga
--- On Thu, 28/4/11, Eik Vettorazzi <e.vettora...@uke.uni-hamburg.de> wrote: From: Eik Vettorazzi <e.vettora...@uke.uni-hamburg.de> Subject: Re: [R] ROCR for combination of markers To: "Rasanga Ruwanthi" <ruwanthi_...@yahoo.com> Cc: r-help@r-project.org Date: Thursday, 28 April, 2011, 13:11 ... and additionally, 'ROC' from the Epi package does the second step all in one. Am 28.04.2011 13:01, schrieb Eik Vettorazzi: > Hi Rasanga, > you may have a look at the 'improveProb' function from the Hmisc > package. There you can compare the increase in prognostic power for > several combinations of markers. You can create a ROC curve for a > combination of markers by using the predicted risks eg. from a logistic > regression model. > > To compare ROC curves of competing markers you can use 'roc.area.test' > from the 'clinfun' package or 'hanley' from gcl. > > hth. > > > Am 27.04.2011 23:17, schrieb Rasanga Ruwanthi: >> Dear list >> >> I have 5 markers that can be used to detect an infection in combination. >> Could you please advise me how to use functions in ROCR/ other package to >> produce the ROC curve for a combination of markers? >> >> I have used the following to get ROC statistics for each marker. >> pred <- prediction(y$marker1, y$infectn) >> perf <-performance(pred,"tpr","fpr") >> plot(perf,ave="threshold",spread.estimate="boxplot") >> >> But I want know whether we could get this for more than one marker, so we >> can look at how good the markers in combination to predict the infection. >> I'm very grateful for any suggestion/help. >> >> Thanks >> Rasanga >> >> >> [[alternative HTML version deleted]] >> >> >> >> >> ______________________________________________ >> 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. > -- Eik Vettorazzi Institut für Medizinische Biometrie und Epidemiologie Universitätsklinikum Hamburg-Eppendorf Martinistr. 52 20246 Hamburg T ++49/40/7410-58243 F ++49/40/7410-57790 [[alternative HTML version deleted]]
______________________________________________ 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.
