Understanding ML Metrics: Recall, Precision, and F1 Score
Analogy: A Fruit Basket
Imagine you have a basket of fruits, and you want to identify all the apples in it.
True Positives (TP): These are the apples you correctly identify as apples. False Positives (FP): These are the fruits you mistakenly identify as apples, but they are actually not apples (e.g., oranges or bananas). False Negatives (FN): These are the apples you fail to identify; you think they are not apples when they actually are.
Definitions
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Recall: This tells you how good you are at finding all the apples in the basket. It’s the ratio of correctly identified apples (TP) to the total number of actual apples (TP + FN).
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Formula: Recall = TP / (TP + FN) Remember: "Recall" is about "recalling" all the true apples.
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Precision: This tells you how many of the fruits you identified as apples are actually apples. It’s the ratio of correctly identified apples (TP) to the total number of fruits you labeled as apples (TP + FP).
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Formula: Precision = TP / (TP + FP) Remember: "Precision" is about being precise in your identification of apples.
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False Positives (FP): This is the number of fruits you incorrectly labeled as apples.
Remember: "False" means you got it wrong, and "Positive" means you said it was an apple.
- False Negatives (FN): This is the number of apples you missed and labeled as something else.
Remember: "False" means you got it wrong, and "Negative" means you said it was not an apple.
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F1 Score: This is a way to combine both precision and recall into a single score. It helps you understand the balance between finding apples (recall) and not mislabeling other fruits as apples (precision).
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Formula: F1 Score = 2 * (Precision * Recall) / (Precision + Recall) Remember: Think of the F1 Score as a "balance" between how well you find apples and how well you avoid mistakes.
Summary
- Recall: How many apples you found (TP) out of all the apples that were there (TP + FN).
- False Positives: How many fruits you wrongly said were apples.
- False Negatives: How many apples you missed.
- F1 Score: A balance between finding apples and not making mistakes.
Using this fruit basket analogy can help you visualize and remember these concepts more easily.