Abstract
IMPORTANCE: Vertical relationships (ownership, affiliations, joint contracting) between physicians and health systems are increasing in the US. Many proponents of vertical relationships argue that increased spending associated with consolidation is accompanied by improvements in quality of care. OBJECTIVE: To assess the association of vertical relationships between primary care physicians (PCPs) and large health systems and quality of care. DESIGN, SETTING, AND PARTICIPANTS: This stacked difference-in-differences study compared outcomes for patients whose attributed PCP entered a vertical relationship with a large system in 2015 or 2017 to patients whose PCP was either never or always in a vertical relationship with a large system from 2013 to 2017. Models account for differences between PCPs, patient characteristics, market concentration, and secular trends. Data were derived from the 2013 to 2017 Massachusetts All-Payer Claims Database. The study population included commercially insured individuals attributed to a PCP in the Massachusetts Health Quality Partners' Massachusetts Provider Database in 2013, 2015, or 2017. Analyses were conducted between January 2021 and January 2024. EXPOSURE: PCPs attributed to patients in the study entering a vertical relationship with a large health system in 2015 or 2017. MAIN OUTCOMES AND MEASURES: Low-value care utilization, posthospitalization follow-up, utilization among patients with ambulatory care-sensitive conditions, practice site visit fragmentation, and timeliness of specialty care. RESULTS: The study population included 4 603 172 patient-year observations from 2013 to 2017. Among all patients in the study, 53.5% were female, 35.3% had any chronic condition, and the mean (SD) age was 38.9 (20.3) years. There was no association between vertical relationships and low-value care or ambulatory care-sensitive conditions utilization. A patient's PCP entering a vertical relationship had no association with the probability of follow-up within 90 days of cancer diagnosis with any oncologist but was associated with a 7.34-percentage point (pp) (95% CI, 2.28-12.40; P = .01) increase in the probability of follow-up with an oncologist in the health system. Vertical relationships were associated with increased posthospitalization follow-up with a physician in the health system by 7.51 pp (95% CI, 2.96-12.06: P = .001) in the 2015 subgroup. PCP-health system vertical relationships were associated with a significant decrease in fragmentation of practice site visits of -1.05 pp (95% CI, -2.05 to 0.05; P = .04). CONCLUSIONS AND RELEVANCE: In this study, vertical relationships between PCPs and large health systems were associated with patient steering and changes in care delivery processes, but not necessarily improvements in patient outcomes.