Is there an advantage? Considerations for researchers studying the effects of the type of Medicare coverage

OBJECTIVE: To describe common methodological problems that arise in comparisons of Medicare Advantage (MA) and Traditional Medicare (TM) and within-MA studies and provide suggestions of how researchers can address these issues. STUDY SETTING: Published research evaluating Medicare coverage options in the United States. STUDY DESIGN: We considered key conceptual challenges and promising solutions that have been used thus far and suggest additional directions. DATA COLLECTION: Not available. PRINCIPAL FINDINGS: Many existing studies of MA versus TM include significant limitations, such as failing to account for unobserved confounders driving both beneficiary coverage choice and health outcomes once enrolled, not accounting for variation in benefit generosity, provider networks, or plan design across MA plans, and/or having been conducted at a time when MA enrollment was less than a third of all Medicare beneficiaries. We provide a review of methods that can help researchers to overcome these weaknesses and suggest additional methods and data sources that may aid future research. CONCLUSIONS: The MA program is becoming an essential part of the US healthcare system. By accounting for non-random movement into and out of MA and studying the heterogeneity of beneficiary experience across plan and market characteristics, researchers can provide the high-quality evidence necessary for policymakers to design the program and reform TM in ways that maximize beneficiary outcomes.