Ever since the first nurse practitioner (NP) was created in 1965, a debate has raged between the medical profession and the advanced practice nursing profession (APRNs) over whether NPs can provide primary care services comparable in quality to physicians. Organizations representing APRNs argue that nurse practitioners receive training that fully qualifies them to provide primary care services. Organizations such as the American Medical Association maintain that “care from nonphysicians is dangerously being promoted as ‘just as good’ as that provided by doctors—despite the huge differences in education and training requirements.”

Both opponents and proponents of expanding nurse practitioners’ scope of practice can cite literature comparing care by NPs to care by physicians. Opponents point to the differences in education and training: physicians must complete 10,000 to 16,000 hours of clinical education and training, while NPs only have 500 to 720 hours. Proponents cite research that NPs provide safe, comparable care to their physician counterparts. Proponents and opponents make these arguments to state lawmakers considering legislation to expand NP scope of practice in their states.

Some physicians claim that NPs make up for their lack of knowledge and experience by ordering too many tests or consulting too many medical specialists, which adds to health care costs. If so, that also makes the argument that, rather than getting in over their heads and risking medical errors, NPs know their limitations and get help when they need it.

It is challenging to study and compare patient outcomes with NPs versus physicians as primary care providers. For example, there’s the matter of self-selection bias, where certain patients may prefer physicians. It is difficult to adjust the data based on the complexity of patients’ conditions. For example, patients who have comorbidities often see specialists. Studies should also consider cost—NPs cost less compared to managed care systems—and access to primary care (in many states, NPs and physician assistants tend to practice in rural and underserved areas).

A recent study by researchers at the University of Washington, the VA Puget Sound Health Care System, and the University of Michigan was designed to minimize confounding factors and offer the best comparison of NP to physician-provided care.

The study used a quasi-experimental approach to examine differences in clinical outcomes, service utilization, and health care costs between NP-assigned and physician-assigned patients. It used administrative data from the Veterans Health Administration (VHA), one of the largest integrated care systems in the U.S..

The VHA reassigned patients whose primary care physician had left the VHA to either another physician or an NP, independent of the patients’ health, introducing a pseudo-random feature to the study. The final sample included 806,434 patients in 530 VHA facilities across the U.S.. After comparing patient conditions pre- and post-reassignment and between primary care providers, the study found NP-assigned patients had similar total costs and clinical outcomes to physician-assigned patients and were less likely to require hospitalization.

The pseudo-random element of the study addresses the confounding variable of sampling bias. The integrated model of the VHA removed the exogenous variables of patient preference and complexity of health status at the time of reassignment. In addition, the study’s large sample size accomplishes a degree of generalizability that other studies have not. This minimizes the effect of independent variables seen in other studies, enabling researchers to better estimate the association between NP-assigned and physician-assigned patient outcomes.

In some states, NPs have full practice authority and independently evaluate, diagnose, and treat patients. Other states restrict their scope of practice, requiring them to work for physicians or have physicians oversee their practice. This new research strengthens the case for expanding NP’s scope of practice to allow them to provide primary care services fully and independently.

Spencer Pratt is a Research Associate in the Department of Health Policy Studies