  The population-attributable fraction (PAF) is a popular epidemiological
measure for the burden of a harmful exposure within a population. It is often
interpreted causally as proportion of preventable cases after an elimination of
exposure. Originally, the PAF has been defined for cohort studies of fixed
length with a baseline exposure or cross-sectional studies.
  An extension of the definition to complex time-to-event data is not
straightforward. We revise the proposed approaches in literature and provide a
clear concept of the PAF for these data situations. The conceptualization is
achieved by a proper differentiation between estimands and estimators as well
as causal effect measures and measures of association.
