How to evaluate a classifier?
The classifier can be evaluated by building the confusion matrix. Confusion matrix shows the total number of correct and wrong predictions. Confusion Matrix for class label positive(+VE) and negative(-VE)is shown below;Actual Class(Target) | |||||
+VE | -VE | ||||
Predicted Class (Model) | +VE | A = True +VE | B = False -VE | +VE prediction | P=A / (A+B) |
-VE | C = False +VE | D = True -VE | -VE prediction | D / (C + D) | |
Sensitivity | Specificity | Accuracy = A + D / (A + B + C + D) | |||
A / (A + C) | D / (B + D) |
Accuracy:
Accuracy is the proportion of the total number of correct predictions. e.g Accuracy = A + D / (A + B + C + D)Error-Rate:
Error Rate = 1 – Accuracy+VE predictions:
+VE predictions are the proportion of the total number of correct positive predictions. +VE predictions = A / (A+B) [quads id=2]-VE predictions:
-VE predictions are the proportion of the total number of correct negative predictions. -VE predictions = D / (C + D)Precision:
Precision is the correctness that how much tuple are- +VE and classifier predicted them as +VE
- -VE and classifier predicted them as -VE
Recall:
Recall = A / Real positive Sensitivity (Recall): Sensitive is the total True +VE rate. The correction of the actual positive cases that are correctly identified. Sensitivity (Recall) = A / (A + C) F-Measure:F-Measure is harmonic mean of recall and precision.
F-Measure = 2 * Precision * Recall / Precision + Recall
Specificity:
Specificity is true -VE rate. Specificity is the proportion of the actual -VE cases that are correctly identified. Specificity = D / (B + D) Note: Specificity of one class is same as the sensitivity of the other class.Next Similar Tutorials
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