DR Medhat MRCP

Q3
MI (event rate ER)
No MI
Blacebo (control) 150/1000 (i.e 15 %) 850/1000 (i.e 85%)
New statin
(Experimental)
100/1000 (i.e 10 %) 900/1000 (i.e 90 %)
- NNT =
- ARR = CER – EER = 15 % - 10 % = 5 %
- So, NNT = 100 / 5 = 20 ( i.e number needed to be treated to prevent one MI is 20)
- In another way :
You treat 1000 patients for five years with the new statin and prevent 50
MIs.
Thus the number needed to treat (NNT) to prevent one MI is 20 (1000/50).
- This statistical figure provides us with a lot of information regarding the efficacy of
a treatment rather than purely statistically significant data.
NNT is a convenient way of describing the results of a randomised controlled
clinical trial and is intuitively more informative than either the relative risk
reduction (RRR) or absolute risk reduction (ARR).
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