A tea-blend grader posts precision of 90% and recall of 60%. What is F1 as 2 × (precision × recall) / (precision + recall), and why is it not the arithmetic mean?
Select an answer to reveal the explanation.
Short Explanation
F1 is 2 times (0.90 times 0.60) / (0.90 + 0.60), which is 1.08 / 1.50, or 72 percent. That is the harmonic mean, high only when both sides are high. 75 percent is the arithmetic mean testers must reject.
Full Explanation
F1 = 2 × (0.90 × 0.60) / (0.90 + 0.60) = 1.08 / 1.50 = 0.72 = 72%. It is the harmonic mean, so both precision and recall must be high. 75% is the simple average testers must reject. 54% and 150% misuse the formula.