PAF is the proportional reduction in population disease or mortality that would occur if exposure to a risk factor were reduced to an alternative ideal exposure scenario.
Many diseases are caused by multiple risk factors, and individual risk factors may interact in their impact on overall risk of disease, hence, PAFs for individual risk factors often overlap and sum to more than 100%
PAF combines both the relative risk of an incident with respect to the factor, as well as the prevalence of the factor in the population.