ROC curves comparison of the AUC's

[FGAB]

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;

[Norman21]

It looks like you are missing a single quotation mark (') in the ROCCONTRAST statement.

[StatDave]

If you have two sets of independent subjects, obese and non-obese, then you can fit separate curves for those two groups and compare the independent ROC curves. To fit the separate curves, specify your OBESE predictor in a BY statement rather than in the CLASS and MODEL statements (also, you should avoid specifying the response in the CLASS statement - it is unnecessary). Then use the method discussed in this note to compare the ROC curves of the independent groups.