A County-level Analysis of the Association Between Medicaid Expansion and Medicare Spending

Background If access to Medicaid improves health outcomes, it may also result in lower long-term spending, however the association between Medicaid expansion and Medicare spending is unknown. In this analysis we sought to investigate the association between Medicaid expansion and per capita Medicare spending at the county level. Methods This is an observational analysis of all U.S. counties in the ten years from 2010 to 2019. We used a difference-in-difference event study to investigate the difference in per capita Medicare spending between counties in states that expanded Medicaid and counties in states that did not expand Medicaid. The exposure was treatment year, which characterized whether a county was in an expansion state and when expansion occurred. In non-expansion counties, treatment year was assigned 0 for all observations. In expansion counties, treatment year ranged from -3 to +6, with treatment year 1 corresponding to the first full year of expansion. The primary outcome was fee-for-service Medicare spending per capita in each county. A secondary analysis investigated subcategories of per capita spending including inpatient, outpatient, skilled nursing care, inpatient rehabilitation, home health, and hospice care. Results We analyzed 1,648 expansion and 1,494 non-expansion counties, with ten observations per county, one for each year between 2010 and 2019. In the adjusted event study analysis, the difference between expansion and non-expansion counties in expansion year 5 compared to pre-expansion was -200 [95% Confidence Interval (CI): -406, 6] dollars. In the subcategory analysis, the difference in inpatient care, skilled nursing care, outpatient care, and home health spending were -46 [95% CI: -103, 12], -92 [95% CI: -194, 11], 57 [95% CI: -67, 181], and 55 [95% CI: -17, 126] dollars per capita respectively. Conclusions Medicaid expansion is not consistently significantly associated with lower Medicare spending compared to pre-expansion. However, observed trends towards lower spending and cost-shifting from inpatient to outpatient settings in expansion counties warrant additional investigation. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This work was supported by grants from the National Institutes of Health [T32 AI007291]. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study used only openly available human data that were originally located at (1) the Centers for Medicare Medicaid Services and (2) the Health Resources and Services Administration: I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors.