Project Summary Every year, more than 20% of Medicare beneficiaries are admitted to the hospital at least once, and these hospitalizations often mark the beginning of more complex health care needs and a trajectory of decline in health. More than 40% of Medicare beneficiaries receive post-acute care (PAC) after a hospital discharge, and 90% of those go either to a skilled nursing facility (SNF) or home with care from a home health agency. The PAC period is often critical in influencing the subsequent trajectory of utilization and outcomes for older adults, such as readmission to the hospital, long-term nursing home entry, and mortality. Persons with Alzheimer's Disease and Related Dementias (ADRD) are twice as likely to be hospitalized as those without ADRD, are more likely to use PAC, and are more likely to suffer post-hospitalization complications. Recent Medicare payment reforms, such as Accountable Care Organizations and bundled payments, have incentivized a reduction in the use and duration of institutional PAC services in favor of home-based services, even for patients with ADRD. Evidence on adverse outcomes from this shift toward home-based PAC is mixed, with some studies showing increased rates of readmission to the hospital under home-based care. Whether home-based PAC results in better outcomes when supports are available in the home and community setting is a critical but unanswered question. For older adults who are dually enrolled in Medicare and Medicaid (duals), a particularly vulnerable population who account for a disproportionate share of both Medicare and Medicaid spending, these supports are often funded by Medicaid in the form of home- and community-based services (HCBS), which has grown rapidly in recent decades. Medicaid HCBS may complement more traditional Medicare-funded home-based in the PAC period, enabling better outcomes. It is also possible that Medicaid HCBS decreases the use of institutional PAC in favor of home-based care. We propose to use rigorous quasi-experimental methods to estimate causal effects of supplementing Medicare- funded PAC with HCBS, which are critically needed to inform PAC provision and policy. We will use county- year-level variation in Medicaid-funded HCBS availability in a longitudinal instrumental variables framework to investigate the role of Medicaid-funded HCBS (overall and by type and intensity) in Medicare-funded PAC utilization and outcomes (readmissions to the hospital, emergency room visits, mortality, long-term nursing home entry, and spending) for older (65+) duals. We will stratify all analyses by ADRD status to reflect the fact that home-based care may be more challenging for people with ADRD and may require a different mix or intensity of services to maximize outcomes. Results from this study will help answer the critical question of whether supplementing home-based PAC with HCBS can both reduce institutional PAC and improve patient outcomes, and will inform policy related to PA...