Abstract
IMPORTANCE: The Outcome and Assessment Information Set (OASIS) is essential for measuring home health quality and outcomes, and accurate linkage between OASIS, Medicare enrollment, and claims is crucial for monitoring utilization and informing payment policy. Preliminary documentation suggested a decrease in OASIS-beneficiary match rates beginning in 2019, but the extent and implications of this decrease have not been quantified. OBJECTIVE: To quantify annual match rates between OASIS assessments and Medicare enrollment and fee-for-service (FFS) home health claims from 2017 through 2023. DESIGN, SETTING, AND PARTICIPANTS: This cohort study used 100% OASIS assessments from 2017-2023 linked to the Master Beneficiary Summary File (MBSF) and FFS home health claims. OASIS assessments included patients receiving home health care in any payer category, while claims analyses were restricted to FFS beneficiaries. Data were analyzed from June 2025 to January 2026. MAIN OUTCOMES AND MEASURES: The yearly number and proportion of OASIS assessments that can be matched to a person in the MBSF and the yearly number and proportion of FFS home health claims that can be matched to an OASIS assessment. RESULTS: Across 2017-2023, approximately 18 million OASIS assessments and 6 million unique assessed beneficiaries were recorded annually. The proportion of assessments linked to a Medicare beneficiary decreased from 89.8% in 2017 to 76.4% in 2023. Among unmatched assessments, the share with Medicare as the recorded payer increased, while the share with Medicaid decreased. For FFS beneficiaries, the number of claims increased due to payment cycle changes, yet the number of unique FFS claimants decreased from 3 424 394 in 2017 to 2 636 931 in 2023. The match rate of FFS claims to an OASIS assessment decreased from 96.8% to 73.9%, with variation across states; by 2023, all state match rates were below 90%. CONCLUSIONS AND RELEVANCE: The findings of this study suggest a reduced ability to accurately attribute OASIS assessments to individual Medicare beneficiaries or matching claims to corresponding OASIS assessments using Centers for Medicare & Medicaid Services (CMS) Research Identifiable Files. Until these issues are addressed by CMS, researchers should cautiously interpret findings utilizing individually linked Medicare claims and OASIS assessment data.