Truncation by death in the sufficient cause framework

TL;DR

This paper uses the sufficient cause framework to analyze truncation by death in epidemiology, clarifying causal estimands and conditions under which effects are null.

Contribution

It provides a new perspective on truncation by death using sufficient causes, linking principal stratification and causal estimands.

Findings

Crude estimand compares distinct risk status types, not causal effects.

Expressions for the crude estimand and survivor average causal effect are derived.

Conditions are identified under which the survivor average causal effect is null.

Abstract

The sufficient cause framework has been used for decades to improve our understanding of both basic and more 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 time of assessment at the end of follow-up. We explain the non-causal 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 the susceptibility to sufficient causes. Further, expressions for the crude estimand and for the survivor average causal effect, 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 survivor average causal effect 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.