Hi All, Thanks for the clarification. Now, perhaps I should use kappa instead. Since my predictions are in 1 and 2, there are no numeric predictions. To my surprise, when I applied kappa and auc to the data, their values are highly correlated, with only an exception when there are perfect predictions for one or both classes. Are there any other accuracy measurements applicable to such predictions with two unbalanced classes? Thanks, Jin -----Original Message----- From: Max Kuhn [mailto:mxk...@gmail.com] Sent: Thursday, 2 June 2011 12:41 PM To: Li Jin Cc: dwinsem...@comcast.net; R-help@r-project.org Subject: Re: [R] aucRoc in caret package [SEC=UNCLASSIFIED]
David, The ROC curve should really be computed with some sort of numeric data (as opposed to classes). It varies the cutoff to get a continuum of sensitivity and specificity values. Using the classes as 1's and 2's implies that the second class is twice the value of the first, which doesn't really make sense. Try getting the class probabilities for predicted1 and predicted2 and use those instead. Thanks, Max On Wed, Jun 1, 2011 at 9:24 PM, <jin...@ga.gov.au> wrote: > > Please note that predicted1 and predicted2 are two sets of predictions > instead of predictors. As you can see the predictions with only two levels, 1 > is for hard and 2 for soft. I need to assess which one is more accurate. Hope > this is clear now. Thanks. > Jin > > -----Original Message----- > From: David Winsemius [mailto:dwinsem...@comcast.net] > Sent: Thursday, 2 June 2011 10:55 AM > To: Li Jin > Cc: R-help@r-project.org > Subject: Re: [R] aucRoc in caret package [SEC=UNCLASSIFIED] > > Using AUC for discrete predictor variables with inly two levels > doesn't seem very sensible. What are you planning to to with this > measure? > > -- > David. > > On Jun 1, 2011, at 8:47 PM, <jin...@ga.gov.au> <jin...@ga.gov.au> wrote: > > > Hi all, > > I used the following code and data to get auc values for two sets of > > predictions: > > library(caret) > >> table(predicted1, trainy) > > trainy > > hard soft > > 1 27 0 > > 2 11 99 > >> aucRoc(roc(predicted1, trainy)) > > [1] 0.5 > > > > > >> table(predicted2, trainy) > > trainy > > hard soft > > 1 27 2 > > 2 11 97 > >> aucRoc(roc(predicted2, trainy)) > > [1] 0.8451621 > > > > predicted1: > > 1 1 2 2 2 1 2 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 1 2 2 2 2 2 2 2 2 2 1 2 > > 2 2 2 2 1 2 2 2 2 1 1 2 2 2 2 2 1 2 2 2 2 2 1 2 2 2 2 2 2 2 2 2 2 2 > > 2 2 2 1 2 2 2 2 2 2 2 1 2 2 2 2 2 1 1 1 2 2 1 1 1 2 2 2 2 2 1 1 2 2 > > 2 2 2 2 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 > > > > predicted2: > > 1 1 2 1 2 1 2 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 1 2 2 2 2 2 2 2 2 1 1 2 > > 2 2 2 2 1 2 2 2 2 1 1 2 2 2 2 2 1 2 2 2 2 2 1 2 2 2 2 2 2 2 2 2 2 2 > > 2 2 2 1 2 2 2 2 2 2 2 1 2 2 2 2 2 1 1 1 2 2 1 1 1 2 2 2 2 2 1 1 2 2 > > 2 2 2 2 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 > > > > trainy: > > hard hard hard soft soft hard hard hard hard soft soft soft soft > > soft soft hard soft soft soft soft soft soft hard soft soft soft > > soft soft soft soft soft soft hard soft soft soft soft soft hard > > soft soft soft soft hard hard soft soft soft hard soft hard soft > > soft soft soft soft hard soft soft soft soft soft soft soft soft > > hard soft soft soft soft soft hard soft soft soft soft soft soft > > soft hard soft soft soft hard hard hard hard hard soft soft hard > > hard hard soft hard soft soft soft hard hard soft soft soft soft > > soft hard hard hard hard hard hard hard soft soft soft soft soft > > soft soft soft soft soft soft soft soft soft soft soft hard soft > > soft soft soft soft soft soft soft > > Levels: hard soft > > > >> Sys.info() > > sysname > > release version nodename > > "Windows" "XP" "build > > 2600, Service Pack 3" "PC-60772" > > machine > > "x86" > > > > I would expect predicted1 is more accurate that the predicted2. But > > the auc values show an opposite. I was wondering whether this is a > > bug or I have done something wrong. Thanks for your help in advance! > > > > Cheers, > > > > Jin > > ____________________________________ > > Jin Li, PhD > > Spatial Modeller/Computational Statistician > > Marine & Coastal Environment > > Geoscience Australia > > GPO Box 378, Canberra, ACT 2601, Australia > > > > Ph: 61 (02) 6249 9899; email: > > jin...@ga.gov.au<mailto:jin...@ga.gov.au> > > _______________________________________ > > > > > > > > [[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. > > David Winsemius, MD > West Hartford, CT > > ______________________________________________ > 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. -- Max ______________________________________________ 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.
