The Precision-Recall Trade-off Game

The Precision-Recall Trade-off Game: Spam Filter

Filter Aggressiveness (Decision Threshold)

Precision0.00

Recall0.00

Score0

Confusion Matrix

Pred Spam

Pred Ham

Actual Spam

—

Actual Ham

—

Scoring Rules

• Correctly caught spam (TP): +5 pts
• Correctly ignored ham (TN): +1 pt
• Blocked real email (FP): -3 pts
• Missed spam (FN): -10 pts

Your Goal: Maximize the score. Each dot is an email. Blue dots are real emails (ham), and red dots are spam. The line is your filter's threshold. Everything to the right of the line is classified as spam. Notice how trying to catch all the spam (high Recall) can cause you to block real emails (lowering Precision). Find the sweet spot!