Is an epidemiological measure. Define as the number of patients who need to be treated for one to get benefit.

Used when an author wants to know how often treatment works.

rather than just, it work.

The reduction of risk (no improvement) with amoxicillin was 20%.

ARR 

Present the difference between the event rate in intervention group and control group.

ARR= CER-EER

NNT=100/ARR.

Number need to treat 

Is an epidemiological measure used in communicating the effectiveness of a health care intervention.

A higher NNT indicates that treatment is less effective.

The ideal 

NNT is 1