Population Attributable Fraction (PAF)

The population attributable fraction is the share of all cases of a disease in a population that would not have occurred if a particular exposure had been absent. For mesothelioma, studies in many countries attribute a large majority of cases, especially in men, to asbestos; for lung cancer the fraction is smaller because smoking causes most cases.

Origin

The measure was introduced by the epidemiologist Morton Levin in 1953 in work on smoking and lung cancer, and it is sometimes called Levin's attributable risk. It is now standard in public-health estimates of the burden of disease caused by occupational and environmental exposures.

Significance in Asbestos Context

Population attributable fractions are how agencies and researchers estimate how many deaths asbestos causes each year. The figure depends on two things: how strongly asbestos raises the risk of a disease, and how many people in the population were exposed. That is why the fraction is high for mesothelioma, where asbestos is by far the main known cause, and lower for lung cancer, where smoking dominates, even though asbestos-exposed workers face a much higher lung cancer risk. The fraction is a population measure. It does not say whether a particular person's cancer was caused by asbestos; that question of specific causation turns on the person's own exposure and medical evidence. Defense experts sometimes cite a lower fraction for women, or for certain types of mesothelioma, to suggest that a case is idiopathic. Lower fractions in some groups may reflect exposures that were never recorded, such as household or environmental contact, so the number must be read with care.

Example Sentence

The national study estimated a population attributable fraction of more than 80 percent for pleural mesothelioma in men, based on lifetime job histories.

Related Terms

Attributable Risk, Relative Risk, Epidemiology, General Causation, Specific Causation, Idiopathic Mesothelioma, Lung Cancer

Notes

• A population figure does not decide whether your own disease was caused by asbestos.
• If a report suggests your disease was not asbestos-related, a detailed exposure history, including household and hobby exposures, can matter.