# Medicine: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.^{[1]} It is calculated as [math]\displaystyle{ AF_e = (I_e - I_u)/I_e = (RR - 1) / RR }[/math], where [math]\displaystyle{ I_e }[/math] is the incidence in the exposed group, [math]\displaystyle{ I_u }[/math] is the incidence in the unexposed group, and [math]\displaystyle{ RR }[/math] is the relative risk.^{[2]}

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,^{[1]}^{[3]} relative attributable risk,^{[1]} attributable proportion among the exposed,^{[1]} and attributable risk among the exposed.^{[4]}

Similarly, attributable risk percent (ARP) is used as a synonym for the attributable risk percent among the exposed.^{[3]}

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.^{[5]}

## Numerical example

Example of risk increase | |||
---|---|---|---|

Experimental group (E) | Control group (C) | Total | |

Events (E) | EE = 75 | CE = 100 | 175 |

Non-events (N) | EN = 75 | CN = 150 | 225 |

Total subjects (S) | ES = EE + EN = 150 | CS = CE + CN = 250 | 400 |

Event rate (ER) | EER = EE / ES = 0.5, or 50% | CER = CE / CS = 0.4, or 40% |

Equation | Variable | Abbr. | Value |
---|---|---|---|

EER − CER | absolute risk increase | ARI | 0.1, or 10% |

(EER − CER) / CER | relative risk increase | RRI | 0.25, or 25% |

1 / (EER − CER) | number needed to harm | NNH | 10 |

EER / CER | risk ratio | RR | 1.25 |

(EE / EN) / (CE / CN) | odds ratio | OR | 1.5 |

(EER − CER) / EER | attributable fraction among the exposed | AF_{e} |
0.2 |

## See also

## References

- ↑
^{1.0}^{1.1}^{1.2}^{1.3}"Dictionary of Epidemiology - Oxford Reference" (in en). Oxford University Press. 2014. doi:10.1093/acref/9780199976720.001.0001. https://www.oxfordreference.com/view/10.1093/acref/9780199976720.001.0001/acref-9780199976720. - ↑ Cole P, MacMahon B (November 1971). "Attributable risk percent in case-control studies".
*Br J Prev Soc Med***25**(4): 242–4. doi:10.1136/jech.25.4.242. PMID 5160433. - ↑
^{3.0}^{3.1}J., Rothman, Kenneth (2012).*Epidemiology : an introduction*(2nd ed.). New York, NY: Oxford University Press. pp. 66. ISBN 9780199754557. OCLC 750986180. - ↑ P., Armitage (2002).
*Statistical methods in medical research*. Berry, G. (Geoffrey), Matthews, J. N. S. (4th ed.). Oxford: Blackwell Scientific Publications. pp. 683. ISBN 9780470773666. OCLC 646751070. - ↑ Peter A. Stott (2013). "Attribution of Weather and Climate-Related Events".
*Climate science for serving society : research, modeling and prediction priorities*. Dordrecht: Springer. pp. 315. ISBN 9789400766921. OCLC 851370783.

Original source: https://en.wikipedia.org/wiki/Attributable fraction among the exposed.
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