A researcher designs a study in which subjects are randomly assigned to either a new antihypertensive drug or placebo and followed for 5 years. At the end of the study, 60 of 300 drug-treated patients had cardiovascular events versus 90 of 300 controls. Calculate the Number Needed to Treat (NNT):
- A 5
- B 8
- C 10 ✓
- D 15
Correct answer: C. 10
Explanation
Event rate in treatment group = 60/300 = 0.20; event rate in control group = 90/300 = 0.30. Absolute Risk Reduction (ARR) = 0.30 − 0.20 = 0.10. NNT = 1/ARR = 1/0.10 = 10. This means 10 patients must be treated to prevent one additional cardiovascular event over 5 years.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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