epidemiology Epidemiology is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in a defined population. It is a cornerstone of public health, and shapes policy decisions and evidenc ...

, preventable fraction among the unexposed (PFu), is the proportion of incidents in the unexposed group that could be prevented by exposure. It is calculated as

PF_u = (I_u - I_e)/I_u = 1 - RR

, where

I_e

is the incidence in the exposed group,

I_u

is the incidence in the unexposed group, and

RR

is the

relative risk The relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group. Together with risk difference and odds ratio, relative risk measures the association bet ...

. It is a synonym of the

relative risk reduction In epidemiology, the relative risk reduction (RRR) or efficacy is the relative decrease in the risk In simple terms, risk is the possibility of something bad happening. Risk involves uncertainty about the effects/implications of an activity with ...

. It is used when an exposure reduces the risk, as opposed to increasing it, in which case its symmetrical notion is

attributable fraction among the exposed In epidemiology, attributable fraction among the exposed (AFe) is the proportion of incidents in the exposed group that are attributable to the risk factor. The term attributable risk percent among the exposed is used if the fraction is expressed as ...

Numerical example

References

{{Clinical research studies Epidemiology Medical statistics

Numerical example

See also

References