MATLAB: Help using perfcurve function!!

aucperfcurveroc

Hey everyone,
I have three groups of people normal ones, one with disease in its early stages and last one people with disease in its severe stages. And in each group I study 16 different features. In order to check the discriminatory performance of several features, I need to use area under the receiver operating characteristic curve. I don't know how can i translate my data to input arguments for the perfcurve function!! [X,Y,T,AUC,OPTROCPT,SUBY,SUBYNAMES] = perfcurve(labels,scores,posclass);
Any help will be appreciated.

Best Answer

Other than a few typos (for example, y1 = (1:132)'>70; clearly is not what you meant), I don't see anything wrong with your code.
glmfit/glmval is your classifier.
The choice of the positive and negative classes is arbitrary. You can always swap them. By convention, the predicted scores must be large for the positive class and small for the negative class. For example, for the first ROC you choose ecan+ as your positive class. Then, I suppose, you set y1 to 1 for ecan+ and 0 for can-. The response returned by your logistic regression model will then be high for ecan+ and low for can-.
You can find many sources (textbooks, web pages etc) that interpret FPR, TPR and AUC.
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