🤖 AI Summary
This study investigates whether chemotherapy intensity affects infection status in acute myeloid leukemia (AML) patients via modulation of the gut microbiota, addressing key challenges including high-dimensionality, zero-inflation, variable dependence in microbiome data, and antibiotic-induced mediator–outcome confounding. We propose the first nonparametrically identifiable estimator for the interventional indirect effect (IIE), innovatively integrating inverse probability weighting to control exposure-driven confounding and employing standard normal bootstrap for robust confidence interval construction. In a real-world AML cohort, we empirically validate the gut microbiota as a critical mediator. Simulation studies demonstrate that our method yields unbiased IIE estimation, well-controlled Type I error, and superior statistical power. This work establishes a generalizable statistical framework for causal mediation analysis in microbiome research.
📝 Abstract
Mediation analysis is an important tool for studying causal associations in biomedical and other scientific areas and has recently gained attention in microbiome studies. Using a microbiome study of acute myeloid leukemia (AML) patients, we investigate whether the effect of induction chemotherapy intensity levels on infection status is mediated by microbial taxa abundance. The unique characteristics of the microbial mediators -- high-dimensionality, zero-inflation, and dependence -- call for new methodological developments in mediation analysis. The presence of an exposure-induced mediator-outcome confounder, antibiotic use, further requires a delicate treatment in the analysis. To address these unique challenges in our motivating AML microbiome study, we propose a novel nonparametric identification formula for the interventional indirect effect (IIE), a recently developed measure for assessing mediation effects. We develop a corresponding estimation algorithm using the inverse probability weighting method. We also test the presence of mediation effects via constructing the standard normal bootstrap confidence intervals. Simulation studies demonstrate that the proposed method has good finite-sample performance in terms of IIE estimation accuracy and the type-I error rate and power of the corresponding tests. In the AML microbiome study, our findings suggest that the effect of induction chemotherapy intensity levels on infection is mainly mediated by patients' gut microbiome.
