Attributable fraction for the population

Illustration of the population, with a part exposed to a risk factor. (AFp = 1/9).
A quarter of the population is exposed to a risk factor (radiation hazard sign) and has a higher risk of an adverse outcome (black). In the whole population, one ninth of the adverse outcomes can be attributed to the exposure (AFp = 1/9).

In epidemiology, attributable fraction for the population (AFp) is the proportion of incidents in the population that are attributable to the risk factor. The term attributable risk percent for the population is used if the fraction is expressed as a percentage.[1] It is calculated as , where is the incidence in the population, and is the incidence in the unexposed group.[1]

Equivalently it can be calculated as , where is the exposed proportion of the population and is the relative risk not adjusted for confounders.[1][2]

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

  1. ^ a b c Porta, Miquel, ed. (2014). "A Dictionary of Epidemiology". Dictionary of Epidemiology - Oxford Reference. Oxford University Press. doi:10.1093/acref/9780199976720.001.0001. ISBN 9780199976720. Retrieved 2018-05-09.
  2. ^ Armitage P, Berry G, Matthews JN (2002). Statistical methods in medical research (4th ed.). Oxford: Blackwell Scientific Publications. p. 682. ISBN 978-0-470-77366-6. OCLC 646751070.