Truncation by death in the sufficient-cause framework

The sufficient-cause framework has been used for decades to improve our understanding of both basic and complex causal concepts in epidemiology, such as mediation and interaction. Here, we make use of this framework to provide a description of truncation by death, in which the outcome of interest is undefined for individuals who die before the assessment time at the end of follow-up. We explain the noncausal nature of the crude estimand that compares outcomes by treatment levels conditional on observed survival by showing that it corresponds to a comparison of distinct risk-status types, which are defined based on their susceptibility to sufficient causes. Further, expressions for the crude estimand and for the survivor average causal effect (SACE)—a causal estimand defined under the principal stratification approach—are provided in terms of population-level joint frequencies of the background factors of sufficient causes. Finally, we also describe conditions, based on background factors of sufficient causes, under which the SACE is null. Our description of this problem, which studies truncation by death from a new perspective, might encourage further analyses of principal stratification-based estimands using sufficient causes.