Table 1.

Definition of measures

Number needed to treat (NNT) "the number of patients who need to be treated to prevent one event" [6] = 1/(Baseline risk * RRR)

Disease Impact Number (DIN) "the number of those with the disease in question amongst whom one event will be prevented by the intervention" [7,8] = NNT * 1/Pe where Pe is the proportion of the diseased population eligible for treatment or; DIN = 1/(baseline risk * RRR * Pe)

Population Impact Number (PIN) "the number of those in the whole population amongst whom one event will be prevented by the intervention" [7,8] = DIN * 1/ Pd where Pd is the proportion of the population with the disease or; PIN = 1/(baseline risk * RRR * Pe * Pd)

Number to be Treated in your Population (NTP) "the number of people in your population who will be eligible for the treatment" = Population size * Pe * Pd

Number of Events Prevented in your Population (NEPP) "the number of events prevented by the intervention in your population" = Population size * Pe * Pd * Baseline risk * RRR (This can also be expressed as: NTP * Baseline risk * RRR; or; NTP * 1/NNT; or Population size/PIN).