The Role of Placebo Samples in Observational Studies

2022/05/22 by Ting Ye, Ye, Ting, Shuxiao Chen +3
Mathematics · #Applications (stat.AP) #FOS: Computer and information sciences #Methodology (stat.ME) #stat.AP #stat.ME

paper · pdf · doi:10.48550/arxiv.2205.10761

arxiv created 2022/07/02 · arxiv updated 2022/07/05

Abstract

In an observational study, it is common to leverage known null effect to detect bias. One such strategy is to set aside a placebo sample -- a subset of data immune from the hypothesized cause-and-effect relationship. Existence of an effect in the placebo sample raises concern of unmeasured confounding bias while absence of it corroborates the causal conclusion. This paper establishes a formal framework for using a placebo sample to detect and remove bias. We state identification assumption, and develop estimation and inference methods based on outcome regression, inverse probability weighting, and doubly-robust approaches. Simulation studies and an empirical application illustrate the finite-sample performance of the proposed methods.

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