Estimating the Size of the Treatment Effect
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Users' Guide: Treatment/Prevention
| Event | |||
| + | - | ||
| Treated | a | b | |
| Untreated | c | d |
EER: Experimental Event Rate: a/(a+b)
CER: Control Event Rate: c/(c+d)
Absolute risk reduction: ARR= CER-EER
Relative risk: RR=EER/CER
Relative risk reduction: RRR=[(CER-EER)/CER]
Number needed to treat: NNT=1/ARR = 1/(CER-EER)
95% Confidence Interval (C.I.) on an NNT = 1/(limits on the C.I.
of its ARR) =
+ or - 1/(1.96 x square root of ((CERx(1-CER)/# control pts.)
/ (EERx(1-EER)/# exper. pts.)))