Eleni Christodoulou wrote: > Richard, thanks, I think it will work. I will calculate the cutoff value > and then, from the prediction object, find the fpr that is related to it and > put it as argument to performance. I will keep you informed. > > Eleni
You will probably need to bootstrap the entire process to get a decent estimate of fpr as your cutoff was not specified in advance. Also note that you are implicitly assuming a constant utility function across all subjects because you are not using probabilities but are ignoring information by creating only a binary prediction. Frank Harrell > > On Wed, Mar 19, 2008 at 11:51 AM, Richard Pearson < > [EMAIL PROTECTED]> wrote: > >> Eleni >> >> Does the fpr.stop argument do what you want? This is described in >> ?performance under the details of the "auc" measure. Try, e.g. >> >> perform=performance(pred,measure="auc",fpr.stop=0.5) >> >> >> Richard. >> >> >> Eleni Christodoulou wrote: >>> Hello list, >>> >>> I am trying to perform ROC analysis and count the AUC in order to >> validate >>> my results. I use package ROCR. I would like to count the AUC not under >> the >>> cutoff found by "performance" but to use another cutoff that I >> calculate. >>> How could I change the following command in order to get what I want? >>> perform=performance(pred,measure="auc",x.measure="cutoff"), where pred >> is a >>> prediction object. >>> >>> Thank you very much, >>> Eleni >>> >>> [[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. >>> >>> >> ______________________________________________ >> 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. >> > > [[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. > -- 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.