Evidence-appraisal glossary
Population attributable fraction
The population attributable fraction (PAF) is the proportion of an outcome in a whole population that would be avoided if a harmful exposure were removed, assuming the exposure causes the outcome. It depends on both how strongly the exposure raises risk and how common the exposure is.
Also called: PAF, population attributable risk fraction, etiologic fraction.
PAF combines the strength of an association with the prevalence of the exposure, so a modest risk factor that is very widespread can account for more cases than a strong risk factor that is rare. It is widely used to argue for public health priorities, since it estimates the share of disease attributable to a given cause across the population. Two cautions apply: the figure assumes the association is causal and that the exposure could be fully eliminated, and because people are exposed to overlapping causes, PAFs for different risk factors can add up to more than 100 percent.
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This is a plain-language methodology definition for reading research. It is general education, not medical advice.