An Expectation-Maximization Algorithm for Domain Adaptation in Gaussian Causal Models

TL;DR

This paper introduces a novel EM-based method for imputing missing target variables in Gaussian causal models under domain shift, leveraging DAG structure for scalable and accurate transfer learning.

Contribution

It develops a first-order EM algorithm that exploits causal DAGs to improve target imputation under covariate and mechanism shifts, with theoretical guarantees and practical scalability.

Findings

The proposed method achieves better imputation accuracy than baseline methods.

The algorithm converges geometrically under standard assumptions.

Experiments demonstrate effectiveness on synthetic and real biological data.

Abstract

We study the problem of imputing a designated target variable that is systematically missing in a shifted deployment domain, when a Gaussian causal DAG is available from a fully observed source domain. We propose a unified EM-based framework that combines source and target data through the DAG structure to transfer information from observed variables to the missing target. On the methodological side, we formulate a population EM operator in the DAG parameter space and introduce a first-order (gradient) EM update that replaces the costly generalized least-squares M-step with a single projected gradient step. Under standard local strong-concavity and smoothness assumptions and a BWY-style \cite{Balakrishnan2017EM} gradient-stability (bounded missing-information) condition, we show that this first-order EM operator is locally contractive around the true target parameters, yielding geometric convergence and finite-sample guarantees on parameter error and the induced target-imputation error in Gaussian SEMs under covariate shift and local mechanism shifts. Algorithmically, we exploit the known causal DAG to freeze source-invariant mechanisms and re-estimate only those conditional distributions directly affected by the shift, making the procedure scalable to higher-dimensional models. In experiments on a synthetic seven-node SEM, the 64-node MAGIC-IRRI genetic network, and the Sachs protein-signaling data, the proposed DAG-aware first-order EM algorithm improves target imputation accuracy over a fit-on-source Bayesian network and a Kiiveri-style EM baseline, with the largest gains under pronounced domain shift.