[R] ROC with more than one predictor

[Luigi]

Dear all,
I would like to perform a receiver operating characteristics (ROC) curve
analysis on data obtained using molecular assays. 

I have here an example: the first column is the sample number, the second is
the response variable and the last three columns are the predictors. I wish
to set the formula to test as R ~ P1 + P2 + P3 in order to obtain the
cut-offs for each of the predictors combined. 

Any tip on how to proceed? 

Thank you
Best regards,
Luigi 

	R	P1			P2	P3
1	0	0.725196908		0	0
2	0	1.089876198		0	0
3	0	1.487365838		0	0
4	0	6.214688703		3.625	0
5	0	48.26356415		13.4	0
6	1	9.494694175		0	0
7	1	15.57700003		4.666	0
8	1	45.53510205		15.57	0
9	1	0.373389928		12.55	1
10	1	0.692909116		0	1
11	1	15.05400384		3.45	1
12	1	20.83909961		6.9	1
13	1	23.24171357		0	1
14	1	43.51470584		0	1
15	1	49.80855616		3.55	1
16	1	664.0886249		10.37	1
17	2	60.85094536		3.725	0
18	2	62.7104185		0	1
19	2	143.7426283		6.5	1