Attributable fraction among the exposed

In epidemiology, attributable fraction among the exposed (AF_e) 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 a percentage. It is calculated as ${\displaystyle AF_{e}=(I_{e}-I_{u})/I_{e}=(RR-1)/RR}$, where ${\displaystyle I_{e}}$ is the incidence in the exposed group, ${\displaystyle I_{u}}$ is the incidence in the unexposed group, and ${\displaystyle RR}$ is the relative risk.

Group exposed to a risk factor (left) has increased risk of an adverse outcome (black) compared to the unexposed group (right). In the exposed group, one third of the adverse outcomes can be attributed to the exposure (AFe = 1/3).

It is used when an exposure increases the risk, as opposed to reducing it, in which case its symmetrical notion is preventable fraction among the unexposed.

Synonyms

Multiple synonyms of AF_e are in use: attributable fraction, relative attributable risk, attributable proportion among the exposed, and attributable risk among the exposed.

Similarly, attributable risk percent (ARP) is used as a synonym for the attributable risk percent among the exposed.

In climatology, fraction of attributable risk (FAR) is used to denote a proportion of adverse event risk attributable to the human influence on climate or other forcing factor.

Numerical example

See also

• Population Impact Measures
• Attributable fraction for the population