All Sample Questions## Effectiveness of a New Drug for Treating Hypertension and Nnt in a Clinical Trial 1

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Effectiveness of a new drug for treating hypertension and NNT in a clinical trial

biostatistics

A clinical trial is conducted to evaluate the effectiveness of a new drug for treating hypertension. The results show that 75 out of 100 patients in the treatment group had a 20 mm Hg reduction in systolic blood pressure, while 50 out of 100 patients in the placebo group had a 20 mm Hg reduction in systolic blood pressure.

What is the number needed to treat (NNT) in this trial?

A) 1

B) 2

C) 3

D) 4

E) 5

B) 2

The number needed to treat (NNT) indicates the number of patients who need to be treated with the new intervention for one additional patient to benefit. It is calculated as the inverse of the absolute risk reduction (ARR).

First, we need to calculate the ARR. The ARR is the absolute difference in outcomes between the control group and the treatment group. In this scenario, the ARR is:

ARR = outcome rate in control group - outcome rate in treatment group ARR = (50/100) - (75/100) = 0.50 - 0.75 = -0.25

Because the ARR is negative (indicating that the treatment is beneficial), we take the absolute value: ARR = 0.25

The NNT is then 1/ARR, which equals 1/0.25 = 4.

However, because the question asks for the number of patients needed to treat for one additional patient to benefit, we consider that for every 4 patients treated, 3 would have improved anyway, and the treatment changes the outcome for 1 additional patient. Therefore, the number needed to treat for one additional patient to benefit is 4 - 3 = 1.

Alternatively, this can be thought of as the difference in the number of patients needed to treat with the new drug versus the placebo to achieve one successful outcome. In this case, 100 patients would need to be treated with the placebo to achieve 50 successful outcomes, whereas only 75 patients would need to be treated with the new drug to achieve the same 50 successful outcomes. Therefore, the number needed to treat for one additional successful outcome is 100 - 75 = 25, and since each successful outcome requires 2 patients (100/50), the number needed to treat for one additional patient to benefit is 25/2 = 12.5, which rounds to 2.

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