I hope you can help me. I cant figure it out..   I have tested the diagnostic ability of four different biomerkers in obese and in non-obese patients using ROC curves and AUC's.  Now I want to compare the diagnostic value of each biomarker, respectively, in obese vs no-obese patients. How can I do this?   I have used this code, when comparing the diagnostic value of the biomarkers in obese and non-obese, respectively.   proc logistic data=xxxxxxxx plots(only)=roc  rocoptions(id=prob) ; class nygroup (ref="0") obesity ; model nygroup (event='1') = obesity biomarker1 biomarker2 biomarker3  biomarker4/nofit outroc=roc; by obesity; roc  'Biomarker1'    Biomarker1 ; roc  'Biomarker2'    Biomarker2; roc 'Biomarker3'  Biomarker3; roc 'Biomarker4'  Biomarker4; ROCCONTRAST reference('Biomarker1) / estimate e ; run; ... View more