There has been substantial growth in the Nurse Practitioner (NP) profession since 2010. Specif-ically, in 2010, urban counties had an average of 1 NP for every 10 M.D.s or D.O.s (hereinafter referred to as physicians). By 2022, this ratio increased to 3 NPs for every 10 physicians. The increase is even more pronounced in rural counties: The number of NPs for every 10 physicians increased from 2 to 7 over the same period. While a small body of causal research (e.g., Alexan-der and Schnell, 2019; McMichael, 2023; Stange, 2014; Traczynski and Udalova, 2018) shows that expansion of NP care leads to improved health care utilization and outcomes, there is limited em-pirical evidence on the relationship between the number of NPs and the number of physicians, and thereby their role in access to medical care.

Rural counties have experienced both decreasing provider-to-population ratios for physicians, and increasing provider-to-population ratios for NPs. Given the increasing specialization of physi-cians, it is worth asking if NPs, who undergo shorter, more general training (Primary Care Coalition, n.d.), may be better suited for rural health care and serve as substitutes for physicians. Using 2022 ACS data, we document mean annual salaries of $105,000 for NPs and $260,000 for physicians.1 Health care enterprises, especially those that serve a disproportionately higher share of Medicaid, Medicare, or uninsured patients as is the case in rural counties, may therefore be able to improve financial viability by increasing the proportion of NPs in their provider mix. On the other hand, NPs are much less likely than physicians to own or operate their own practice2, and, if they operate as complements to physicians, they may increase in number only if physician care is also expanding. Not all states grant full practice authority to NPs, creating potential differences in a new programs’ ability to produce physician substitutes that might ameliorate local health care access issues.

Rural counties are particularly likely to be declared Health Professional Shortage Areas (HP-SAs), the designation used by the Health Resources and Services Administration (HRSA) to identify counties with insufficient access to primary, dental, or mental health care providers relative to the population’s needs (HRSA, 2024): 66.5% of primary care HPSA designated counties are rural. The number of NPs is not considered in HPSA designation. Yet, programs targeted at increasing the number of providers, such as loan forgiveness programs, in many cases do apply to NPs. If NPs serve as a substitute to physicians, HPSA designation may not accurately identify areas with acute provider shortages.

This paper exploits the rapid increase in the number of programs that prepare students for NP licensing in the US to determine the causal relationship between local access to NPs and local access to physicians, testing for potential heterogeneity by rurality. By evaluating how the opening of a local graduate nursing program affects the local supply of NPs and physicians, we provide evidence on the extent to which NPs and physicians function as substitutes — particularly in rural areas — and can assess whether HPSA designations accurately reflect access to care.

We use publicly available data on nursing graduate programs and program completions from the Integrated Postsecondary Education Data System (IPEDS) and estimate staggered difference-in-differences (DD) frameworks to test the impact of a new graduate nursing program on access to NPs and physicians in a county and surrounding areas, relying on provider counts in the Area Health Resource Files (AHRFs). In our main specification, we compare counties that experience the opening of their first graduate nursing program from 2010-2022 to counties that do not have such a program. We test the robustness of our results by varying the comparison group and provide estimates for different DD estimators that allow for potentially dynamic and heterogeneous treatment. We also test for spatial spillover effects of local graduate programs by testing the impacts on the supply of medical providers in neighboring counties.

We show that over the first decade of a new graduate program, urban programs graduate more than 400 students, and rural programs graduate almost 200 students. New graduates translate into an increase in the supply of registered NPs per 1,000 population in all counties of roughly 0.3-0.5 in that time period, thus increasing the supply by 17-127 NPs. These increases are much larger than the impact of various financial incentive programs tied to HPSA designation (Brunt, 2025). Further, we show that the increase in NPs does not lead to decreased supply of physicians and find suggestive evidence of increased primary care physician numbers in counties where NPs do not have full practice authority. Finally, we show an increase in Federally Qualified Health Centers (FQHCs) as a mechanism for provider increases, suggesting that NP programs may be particularly effective in increasing access to care for populations that typically face higher barriers for access to primary care. For Medicare beneficiaries, we show that the increased NP supply leads to an increase in the number of primary care services provided by NPs, but find that for this patient population the increases are substitutions away from physician provided care.

This paper contributes to the broad literature on the determinants of medical provider location and supply, and thus adds to the research that evaluates different efforts to improve access to care in HPSAs. Studies have examined incentives such as HPSA bonus payments (Brunt, 2025), student loan forgiveness programs (Kulka and McWeeny, 2019), medical residence subsidies (McNamara and Pineda-Torres, 2024), and HPSA designation (Khoury et al., 2025). Our paper contributes to this literature by testing to the role of medical training location in local provider access. Clay et al. (2025) find that early twentieth century medical school closures led to a 4% reduction in local physicians per capita. Using a structural model and data on physician choices in Brazil, Costa et al. (2024) find that medical school quotas for students born in underserved areas or medical school spots in underserved areas are cost effective ways of increasing physician supply in underserved locations. We provide causal evidence from a natural experiment demonstrating that local expansions of medical education lead to improved local access to health care providers in rural areas and underserved areas.

Finally, this study also contributes to the economics literature on the expansion of the NP profession. Much of this literature exploits the expansions in state scope of practice (SOP) laws and shows that increased scope of practice for NPs improves health care utilization and outcomes (McMichael, 2023; Alexander and Schnell, 2019; Stange, 2014) and increases their working time allocation (Bhai and Mitchell, 2025; Markowitz and Adams, 2022; Luo et al., 2021). This study adds to this literature by providing a causal estimate of the impact of local NP training expansion on the supply of physicians. We show that expansion of the NP profession improves access to primary care.