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Calculate Accuracy, Precision, Recall and F1 Score for the following Confusion Matrix on Heart Attack Risk. Also suggest which metric would not be a good evaluation parameter here and why?

Topic - Evaluation

Type - Long answer (4 Marks) 

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The Confusion Matrix Reality: 1 Reality: 0
Prediction: 1 50 20
Prediction: 0 10 20

The Confusion Matrix Reality: 1 Reality: 0
Prediction: 1 50 20 70
Prediction: 0 10 20 30
60 40 100

Calculation: 

Accuracy: Accuracy is defined as the percentage of correct predictions out of all the observations

Accuracy = Correct Predictions / Total Cases * 100%

Accuracy = (TP + TN) / (TP + TN + FP + FN +) * 100%

Where True Positive (TP), True Negative (TN), False Positive (FP) and False Negative (FN). Accuracy = (50+20) / (50+20+20+10) = 

(70/100) = 0.7 

Precision: Precision is defined as the percentage of true positive cases versus all the cases where the prediction is true. 

Precision = True Positive / All Predicted Positives * 100%

Precision = TP / (TP + FP) * 100%

= (50 / (50 + 20)) = (50/70) = 0.714

Recall: It is defined as the fraction of positive cases that are correctly identified

Recall = True Positive / True Positive + False Negative 

Recall = TP / TP + FN 

= 50 / (50 + 60) = 50 / 110 = 0.5

F1 score is defined as the measure of balance between precision and recall.

F1 Score = 2 * Precision * Recall / Precision + Recall 

= 2 * (0.714 *0.5) / (0.714 + 0.5) = 2 * (0.357 / 1.214)

= 2* (0.29406) = 0.58

Therefore,

 Accuracy= 0.7 , Precision=0.714 ,  Recall=0.5 , F1 Score=0.588 

Here within the test there is a tradeoff. But Recall is not a good Evaluation metric. Recall metric needs to improve more.

Because, False Positive (impacts Precision): A person is predicted as high risk but does not have heart attack.

False Negative (impacts Recall): A person is predicted as low risk but has heart attack. Therefore, False Negatives miss actual heart patients, hence recall metric need more improvement. False Negatives are more dangerous than False Positives. 


Study more about Evaluation at Evaluation Class 10

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