DR Medhat MRCP

Statistics which compare risk
RISK REDUCTION AND
NUMBERS NEEDED TO TREAT
Absolute risk reduction (ARR) :
- Is the difference between the event rate in the experimental group and that in
the control group.
ARR = experimental event rate (EER)- control event rate (CER)
- It is also the reciprocal of the NNT and is usually given as a percentage,
ARR =
NNT is the number of patients who need to be treated for one to get benefit.
Relative risk reduction (RRR) :
- Is the proportion by which the experiment (e.g drug) reduces the event rate.
RRR = X 100
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