How to draw ROC curve using value of confusion matrix?

Question

Consider i have a classifier like A and the result of its classification gives me the following table:

    TP  TN  FP  FN
A   225 100 175 100
         


        

Answer 1

This is impossible, because you only have a confusion matrix for a certain (unknown) threshold of your classifier. A ROC-Curve contains information about all possible thresholds.

The Confusion matrix corresponds to a single point on your ROC Curve:

Sensitivity = TP / (TP + FN)
1 - Specificy = TN / (TN + FP) .