Precision vs Recall

Precision:

• \(\frac{\text{true positives}}{\text{true positives} + \text{false positives}}\).
• "Out of all the examples that you grabbed, how many were correct?"
• If you know one correct answer, you can get perfect precision by just grabbing that answer.

Recall:

• \(\frac{\text{true positives}}{\text{true positives} + \text{false negatives}}\).
• "Out of all the correct examples in the pool, how many did you grab?"
• You can get perfect recall by just grabbing all the examples.

For other common measures of detector performance see the receiver operating characteristic note.