A randomized controlled clinical trial was performed to evaluate the effect of a new hormone called Rejuvenon on mortality in septic shock. 3400 patients with septic shock were studied (1700 placebo and 1700 in the Rejuvenon arms). The mortality rates in the placebo and the treatment arms were 30% and 25% respectively.

Calculate:

(a) The absolute risk reduction

(b) The relative risk reduction

(c) The number needed to treat

## College Answer

Using the above data, show how you would calculate:

a) The absolute risk reduction

b) The relative risk reduction

c) The number needed to treat

ARR = 5%

RRR = 5/30*100 =16.6%

NNT =1/0.05 =20

## Discussion

This question also relies on the candidate's ability to memorise equations.

Here is a helpful list of equations the candidate is expected to memorise.

**a) ARR = (risk in control group - risk in treatment group)**

= 30% - 25%

= 5%

**b) RRR = (ARR / control group AR)**

= 0.05 / 0.3

= 0.166, or 16.6%

**c) Numbers needed to treat (NNT) = ( 1/ ARR)**

= 1 / 0.05

= 20.