The F-score, or F1, combines precision and recall into one metric using their harmonic mean: F = 2 × (precision × recall) / (precision + recall). section 8.9
It is useful when you want one summary of both kinds of performance, but it gives precision and recall equal importance—even when a real decision favors one. section 8.9
The wolf alarm
An alarm that triggers for everything catches wolves but produces many false alarms, driving precision toward zero. An alarm set extremely high may catch one wolf correctly, reaching perfect precision while recall approaches zero. The F-score summarizes this tension, but choosing the right balance still depends on the business case. section 8.9
