Inference in Cluster Randomized Trials with Matched Pairs

TL;DR

This paper analyzes inference methods in cluster randomized trials with matched pairs, proposing consistent variance estimators, evaluating test procedures, and introducing covariate adjustment to improve precision.

Contribution

It develops a unified variance estimator, assesses the validity of common tests, and proposes a covariate-adjusted estimator for matched-pair cluster trials.

Findings

Proposed a variance estimator consistent across matching regimes.

Found that t-tests are generally conservative in this setting.

Demonstrated the effectiveness of covariate adjustment in simulations.

Abstract

This paper studies inference in cluster randomized trials where treatment status is determined according to a "matched pairs" design. Here, by a cluster randomized experiment, we mean one in which treatment is assigned at the level of the cluster; by a "matched pairs" design, we mean that a sample of clusters is paired according to baseline, cluster-level covariates and, within each pair, one cluster is selected at random for treatment. We study the large-sample behavior of a weighted difference-in-means estimator and derive two distinct sets of results depending on if the matching procedure does or does not match on cluster size. We then propose a single variance estimator which is consistent in either regime. Combining these results establishes the asymptotic exactness of tests based on these estimators. Next, we consider the properties of two common testing procedures based on t-tests constructed from linear regressions, and argue that both are generally conservative in our framework. We additionally study the behavior of a randomization test which permutes the treatment status for clusters within pairs, and establish its finite-sample and asymptotic validity for testing specific null hypotheses. Finally, we propose a covariate-adjusted estimator which adjusts for additional baseline covariates not used for treatment assignment, and establish conditions under which such an estimator leads to strict improvements in precision. A simulation study confirms the practical relevance of our theoretical results.