Adjusting for Unmeasured Spatial Confounding with Distance Adjusted Propensity Score Matching

TL;DR

This paper introduces DAPSm, a novel method that integrates spatial proximity into propensity score matching to better control for both observed and unmeasured spatial confounding in observational studies.

Contribution

The paper develops and evaluates DAPSm, a new approach that incorporates spatial information into propensity score matching to address unmeasured confounding in spatial data.

Findings

DAPSm effectively adjusts for unmeasured spatial confounding.

DAPSm outperforms traditional methods in spatial confounding scenarios.

Application to ozone pollution data demonstrates practical utility.

Abstract

Propensity score matching is a common tool for adjusting for observed confounding in observational studies, but is known to have limitations in the presence of unmeasured confounding. In many settings, researchers are confronted with spatially-indexed data where the relative locations of the observational units may serve as a useful proxy for unmeasured confounding that varies according to a spatial pattern. We develop a new method, termed Distance Adjusted Propensity Score Matching (DAPSm) that incorporates information on units' spatial proximity into a propensity score matching procedure. We show that DAPSm can adjust for both observed and some forms of unobserved confounding and evaluate its performance relative to several other reasonable alternatives for incorporating spatial information into propensity score adjustment. The method is motivated by and applied to a comparative effectiveness investigation of power plant emission reduction technologies designed to reduce population exposure to ambient ozone pollution. Ultimately, DAPSm provides a framework for augmenting a "standard" propensity score analysis with information on spatial proximity and provides a transparent and principled way to assess the relative trade offs of prioritizing observed confounding adjustment versus spatial proximity adjustment.