Many states in the U.S. have shortages of primary care doctors, with this shortage projected to grow in the future. Primary care providers (PCPs) offer regular preventative medical care, reducing the number of routine problems that end up in emergency room visits and keeping chronic conditions from worsening until a hospital stay is required. A lack of PCPs can both harm population health and increase state medical expenditures.

One potential solution to the shortage of PCPs is for states to give increased independence to nurse practitioners (NPs). A number of randomized trials have concluded that patients using NPs for primary care have comparable health outcomes to patients who use doctors. Allowing NPs to manage relatively simple ailments without the supervision of a doctor may free up more of the doctor's time to work on cases where more advanced training will have a larger marginal impact on patient health. Since NP training is less costly than training for doctors, allowing NPs the flexibility to handle primary care may represent cost savings for a state looking to increase its number of PCPs. Recently, the Affordable Care Act has provided additional funding for NP education and demonstration projects, partially to explore this possibility.

Increasing the autonomy of NPs decouples the geographic location of nurse practice from the location of the doctors. Since the shortage of primary care doctors can be particularly acute in rural areas, allowing NPs to practice independently may lead to better health outcomes in traditionally underserved areas. The ability of an NP to write prescriptions for common illnesses without needing a doctor's approval may further increase the NP's ability to serve as a PCP in an area with few doctors, especially when treating patients with chronic illnesses that require drug treatment such as diabetes or hypertension.

We estimate the effect of NP autonomy on health outcomes by exploiting plausibly exogenous state level variation in regulations governing the level of supervision that doctors must provide for NPs. Identification of this effect comes from within state variation in regulations over time. We examine the effect of regulations on NP independent practice as well as NP prescribing authority. As some states have allowed NPs to practice or prescribe independently for longer periods of time, we investigate the difference between short and long run effects of NP independence. We also look for potential differences in the populations affected by NP independence, such as whether individuals in rural areas, without medical insurance, or in states with a higher ratio of NPs to doctors benefit differentially.

Preliminary results suggest that states that allow NPs to practice independently see improvements in the self-reported health status of the population over a longer timeframe (5+ years), as well as decreases in the number of emergency room visits. There is also evidence of potential causal mechanisms, as NP autonomy is associated with more frequent checkups and basic diagnostic testing.