Role of Patient Sorting in Avoidable Hospital Stays in Medicare Advantage vs Traditional Medicare

IMPORTANCE: Unlike traditional Medicare (TM), Medicare Advantage (MA) plans limit in-network care to a specific network of Medicare clinicians. MA plans thus play a role in sorting patients to a subset of clinicians. It is unknown whether the performance of physicians who treat MA and TM beneficiaries is different. OBJECTIVE: To examine whether avoidable hospital stay differences between MA and TM can be explained by the primary care clinicians who treat MA and TM beneficiaries. DESIGN, SETTING, AND PARTICIPANTS: This was a cross-sectional study of a nationally representative sample of MA and TM beneficiaries in 2019 with any of 5 chronic ambulatory care–sensitive conditions (ACSCs). The relative risk (RR) of avoidable hospital stays in MA compared with TM was estimated with inverse probability of treatment-weighted Poisson regression, both without and with clinician fixed effects. The degree to which the estimated MA vs TM difference could be explained by patient sorting was calculated by comparing the 2 RR estimates. Data were analyzed between February 2022 and April 2023. EXPOSURE: Enrollment in MA. MAIN OUTCOME AND MEASURES: Whether a beneficiary had avoidable hospital stays in 2019 due to any of the ACSCs. Avoidable hospital stays included both hospitalizations and observation stays. RESULTS: The study sample comprised 1 323 481 MA beneficiaries (mean [SD] age, 75.4 [7.0] years; 56.9% women; 69.3% White) and 1 965 863 TM beneficiaries (mean [SD] age, 75.9 [7.4] years; 57.1% women; 82.5% White). When controlling for the primary care clinician, the RR of avoidable hospital stays in MA vs TM changed by 2.6 percentage points (95% CI, 1.72-3.50; P < .001), suggesting that compared with TM beneficiaries, MA beneficiaries saw clinicians with lower rates of avoidable hospital stays. This effect size was statistically significant to explain the 2% lower rate of avoidable hospital stays in MA than in TM. CONCLUSIONS AND RELEVANCE: In this cross-sectional study of MA and TM beneficiaries, the lower rate of avoidable hospital stays among MA beneficiaries than TM beneficiaries was attributable to MA beneficiaries visiting clinicians with lower rates of avoidable hospital stays. The patient sorting that occurs in MA plays a critical role in the lower rates of avoidable hospital stays compared with TM.