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Wiki/Machine Learning/Model Validation and Evaluation.md

@@ -73,4 +73,6 @@ When using it in this context a value of 1 represents a perfect classifier (mode
 ### ROC and AUC
 ROC stands for the Receiver-operating characteristic curve. The graph is found by plotting the true positive rate on the y-axis and the false positive rate on the x-axis as the threshold changes. This is a parametric graph with the threshold as the parameter.
 ![[rocCurve.excalidraw]]
-A perfect classifier is represented by a point at $(0, 1)$ which means that every prediction is correct (no false positives). A straight line from $(0, 0)$ to $(1, 1)$ repres
+A perfect classifier is represented by a point at $(0, 1)$ which means that every prediction is correct (no false positives). A straight line from $(0, 0)$ to $(1, 1)$ represents a random classifier (same number of true and false positives). Curves will generally look like the green or blue ones with blue performing better than a random classifier and green performing worse.
+
+The area under the ROC curve (AUC) represents the probability that given random positive and negative examples it will rank the positive example above the negative one. A perfect classifier has a AUC of 1.0 meaning that it will always put a positive instance above a negative one thus separating the two classes.