ARR & NNT Flashcards
1
Q
What is Absolute Risk Reduction (ARR)?
A
The difference between the event rate in the intervention group and that in the control group.
(e.g. 50 in tx group. 40 get better.
50 in control group. 30 get better.
THEREFORE ARR = 80%(40/50) - 60% (30/50) = 20%
2
Q
What is the Number Needed to Treat (NNT)?
A
The number of patients who need to be treated for one to get benefit.
NNT = 100/ARR
If ARR is 20% then
NNT = 100/20 = 5
5 needed to be treated for 1 to get benefit.
3
Q
If a person’s AR of stroke, estimated from his age and other risk factors, is 0.25 without treatment but falls to 0.20 with treatment, what is the ARR?
What is the RRR?
What is the NNT?
A
The ARR is 25% – 20% = 5%.
The RRR is (25% – 20%) / 25% = 20%.
The NNT is 1 / 0.05 = 20.
