The population impact number from eliminating a risk factor for a given period of time t (PIN-ER-t) can be used to help communicate the impact of removing a risk factor for a disease. This incorporates the population attributable risk (PAR) described in the previous section. Since a condition may have several risk factors, this helps describe the benefit of removing a single one.
Parameters:
(1) population size
(2) incidence of the outcome event (target disorder) in the whole population over t years
(3) population attributable risk (derived from (a) the relative risk of the outcome event if the risk factor is present and (b) the proportion of the population exposed to the risk factor)
PIN-ER-t =
= (population size) * (incidence over t years) * (PAR)
Limitations:
• The estimate assumes that the risk factor can be totally eliminated from the population. If this is not possible, then the number will overestimate the number actually seen.
• For a risk factor that is cumulative and which takes years to cause an effect, removing the risk factor for a comparatively short time interval might overestimate the number actually seen.
• Accurate predictions for a given population requires accurate data in that population.
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