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When we generate ROC curves from Weka, curve is displayed in a color scale. I understand what is a ROC curve. But what is the meaning of the color scale in this ROC curve?

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manu
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  • It's the class... Just like it says! – SJB Nov 15 '15 at 12:32
  • yes I can see that. What I am asking is what does that imply? As I know different points in curve are pairs of (false positive rate, true positive rate)for different threshhold values. Is not it? so y color code this curve according to a class code? what does that mean? – manu Nov 15 '15 at 14:06
  • does it represent the threshold values? – manu Nov 15 '15 at 14:08
  • @Campino - no, it is not "a class" in any sense. – lejlot Nov 15 '15 at 14:30

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Color depends on what have you chosen. In your case, you chosen Colour: Threshold, so the color represents threshold value set to get this pair of true FPR/TPR point.

In other words - ROC is a parametric curve of the threshold, so point (tpr, fpr) belongs to ROC if and only if there exists threshold value t for which experiment results in True positive rate=tpr and False positive rate=fpr. However, it is just an existance, so ROC as such does not show what is the exact value of t used. Coloring the curve gives you this one missing information.

lejlot
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