The R Package WMAP: Tools for Causal Meta-Analysis by Integrating Multiple Observational Studies

TL;DR

The WMAP R package provides tools for causal meta-analysis by integrating multiple observational studies, estimating propensity scores, and calculating effective sample sizes to improve causal inference across diverse groups.

Contribution

It introduces a unified weighting framework with three approaches, including the novel FLEXOR method, for causal meta-analysis in observational studies.

Findings

Effective estimation of propensity scores and weights

Improved effective sample size with FLEXOR method

Successful application to breast cancer multi-site study

Abstract

Integrating multiple observational studies for meta-analysis has sparked much interest. The presented R package WMAP (Weighted Meta-Analysis with Pseudo-Population) addresses a critical gap in the implementation of integrative weighting approaches for multiple observational studies and causal inferences about various groups of subjects, such as disease subtypes. The package features three weighting approaches, each representing a special case of the unified weighting framework introduced by Guha and Li (2024), which includes an extension of inverse probability weights for data integration settings. It performs meta-analysis on user-inputted datasets as follows: (i) it first estimates the propensity scores for study-group combinations, calculates subject balancing weights, and determines the effective sample size (ESS) for a user-specified weighting method; and (ii) it then estimates various features of multiple counterfactual group outcomes, such as group medians and differences in group means for the mRNA expression of eight genes. Additionally, bootstrap variability estimates are provided. Among the implemented weighting methods, we highlight the FLEXible, Optimized, and Realistic (FLEXOR) method, which is specifically designed to maximize the ESS within the unified framework. The use of the software is illustrated by simulations as well as a multi-site breast cancer study conducted in seven medical centers.