I found the ROC explanation at this link. It states that the ROC curve is TP
vs FP
.
After the score
has gone below 0.5
, all predictions are negative
. That makes them either TN
or FN
. Thus, how does it make sense to continue drawing as the axes are stated as TP
and FP
? I am really confused.
Best Answer
The ROC curve shows the TPR and FPR as you change the threshold. Your question posits that a classifier only has one TPR statistic and one FPR statistic, and that both of these statistics correspond to a threshold at 0.5. This is a common misconception; there is no reason that the threshold must be 0.5. For each choice of threshold, there is a corresponding TPR and FPR statistic. The purpose of the ROC curve is to show the trade-off for each choice of threshold: as your TPR increases, so does your FPR, and vice-versa.