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Population attributable fraction: names, types and issues with incorrect interpretation of relative risks
  1. Belen Zapata-Diomedi1,
  2. Jan J Barendregt2,3,
  3. J Lennert Veerman3
  1. 1 School of Public Health, The University of Queensland, Brisbane, Queensland, Australia
  2. 2 Epigear International, Sunrise Beach, Queensland, Australia
  3. 3 School of Public Health, The University of Queensland, Brisbane, Queensland, Australia
  1. Correspondence to Belen Zapata-Diomedi, School of Public Health, The University of Queensland, Level 2, Public Health Building, Herston, Brisbane, QLD 4006, Australia; b.zapatadiomedi{at}

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The development of the original population attributable fraction (PAF) dates back to 19531 and it has been widely used, misused and miscalled since then. We discuss two main issues here: use of appropriate terminology and calculations of the PAF, and of the potential impact fraction (PIF).

The PAF is the proportion of cases for an outcome of interest that can be attributed to a given risk factor among the entire population.2 Despite this clear description, it is not rare to find studies that call it population attributable risk (PAR). PAR is the difference in the rate or risk of disease for the population compared to the unexposed.Embedded Image 1 Embedded Image 2

PAR is only one of the other names being used; as noted previously,3 ,4 there is great vagueness in the use of terminology. Other common names used are ‘population attributable risk percent’, ‘excess fraction’, ‘etiological fraction’ and ‘attributable fraction’. …

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  • Contributors BZ-D drafted the manuscript with the assistance of JJB. JJB and JLV commented on the manuscript and edited manuscript. BZ-D finalised the manuscript for submission.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.