On the Identification of the Survivor Average Causal Effect

Abstract

In randomized trials in which the outcome requires considerable follow-up, participants may die before the trial is complete. In such cases, for the individuals who die before follow-up is complete, the outcome is not simply missing, but is undefined. Some authors refer to this situation as one in which the outcome is “truncated by death� [1,2], to distinguish this scenario from cases in which the outcome is merely missing because of inadequate data collection. In these settings, a crude comparison of the outcome between those who survived in each treatment arm may give misleading results, because we no longer preserve randomization by conditioning on a post-treatment event (survival) and thus the crude comparison is not a comparison for the same population comparing different treatments, but a comparison of different populations.