A supplied antiemetic comparison
A fictional randomized educational dataset follows two comparable groups over the same specified postoperative interval. Nausea or vomiting occurs in 20 percent of the control group and 10 percent of the intervention group. For this arithmetic exercise, the stated event probabilities are treated as exact and adherence and follow-up are assumed complete. A learner calls the absolute reduction 50 percent because the treated event rate is half the control rate. Another reports a number needed to treat of 2. The instructor asks for the absolute and relative quantities to be separated before discussing uncertainty or external validity. No claim is made that the intervention is suitable for every real patient.
1. Calculate the absolute reduction and NNT.
Read the worked answer
The absolute reduction is 0.20 - 0.10 = 0.10, or 10 percentage points. NNT is 1 / 0.10 = 10 over the supplied follow-up.
2. What does the 50 percent figure represent?
Read the worked answer
It is the relative risk reduction, calculated as 0.10 / 0.20. It is not the absolute reduction and does not imply an NNT of 2.