Physician assistants and nurse practitioners: the United States experience

Roderick S Hooker
Med J Aust 2006; 185 (1): 4-7. || doi: 10.5694/j.1326-5377.2006.tb00438.x
Published online: 3 July 2006
Characteristics of PAs and NPs

As of 2006, there are about 110 000 clinically active PAs and NPs in the US, comprising about one sixth of the US medical workforce. Numbers are equally divided between the two groups. The mean age is 41.5 years for PAs and 46 years for NPs, with women making up about 60% of PAs and 90% of NPs. About 90% of PAs and 50% of NPs work full-time (> 32 hours per week).3

The settings in which NPs and PAs work are diverse and include individual and group practices, urban and rural areas, hospitals, battalion-aid stations, correctional institutions, inner city clinics, migrant worker clinics, emergency medical departments, and other typical doctor offices. Many PAs and NPs are employed by large capitated managed-care organisations. Almost a quarter of all PAs and NPs are located in non-metropolitan areas, often in communities with populations smaller than 10 000.4

About 50% of PAs and 85% of NPs practise in primary care (defined as general internal medicine, family medicine, general paediatrics and women’s health), compared with 30% of doctors. The remaining NPs and PAs work in the non-primary care discipline of surgery (including general surgery, cardiovascular surgery, orthopaedics and emergency medicine) and medical subspecialties (eg, occupational and environmental medicine, neonatology, oncology, psychiatry and acute care). In specialised medical services, PAs are more likely than NPs to work in surgical specialties, while NPs are more likely than PAs to work in paediatrics and women’s health.

Qualifications for practice and legal parameters

The licensure of health professionals in the US is the responsibility of the 50 states, five territories and the District of Columbia, rather than the federal government. These licensing regulations are tailored as individual medical statutes that define the scope of practice activities. Entry to practise as an NP or PA requires a uniform set of characteristics: certification of graduation from an accredited program, and a passing score on a certifying examination.5

Clinical professional activities and scope of practice are regulated by individual state licensing boards — usually the state medical board for PAs, and the state board of nursing for NPs. While NPs are professionally autonomous in the performance of nursing care functions, in most states they are required to work in collaboration with a physician, recognising that their extended roles encompass medical diagnostic and therapeutic tasks. However, in 16 states, they may practise independently and, in 11 of these, they may also prescribe independently. In contrast, all PAs are required to work under the delegated authority of a physician supervisor. However, most states allow practice at a distance from the supervising physician as long as some form of communication is maintained. This allows PAs to work in rural and under-served areas — for example, in satellite clinics.

“Scope of practice” includes the roles, responsibilities, duties and range of services a clinician may perform. For some jurisdictions, this scope is broadly or expansively defined. In others, the definition may be so highly detailed that it restricts the performance of daily tasks. While in many instances the statutes are fairly equal for PAs and NPs, the scope-of-practice legislation can sometimes provide a competitive edge for one profession over the other.6


Historically, PA and NP tracks started as certificate programs, but have evolved, with most now at graduate level, awarding master’s degrees.10 Most programs are on the same campus as a medical or nursing school.11


The literature on PA and NP productivity (measured as efficiency and cost effectiveness) is growing. An analysis of the early economic research on the impact of PAs on rural or solo practices generally found a PA to be an asset. PAs increased productivity in terms of the number of patients seen, and improved the workload and income of the employing doctor.12 A comparison of the productivity of PAs/NPs and physicians in internal medicine, family medicine, obstetrics and gynaecology, paediatrics and orthopaedics revealed that PAs/NPs generally saw 10% more patients annually in the ambulatory setting than doctors. This was because doctors’ collateral roles and hospital responsibilities took them out of the clinic. However, the productivity based on number of patients seen per hour was the same for all three types of provider.13

NPs have been shown to provide primary care services comparable to physicians in particular settings, as exemplified by the study of Mundinger and colleagues.14 In a randomised study of follow-up care for patients who presented to a hospital emergency department and who had no personal physician, care delivered by physicians and NPs showed similar outcomes at 1 year in terms of clinical status and patient satisfaction. While some authors have criticised this work based on the demographic characteristics of the population (90% Hispanic, 77% female, and largely poor), it does suggest that the roles of NPs are probably undervalued.15

In another example, a family practice model was intensively studied to identify the trade-off between employing a PA versus another doctor. The PA had a “same task” substitution ratio of 0.86, compared with the supervising physician (ie, the PA saw the same types of patients and rendered the same care as the physician 86% of the time). Overall, the PA was economically beneficial to the practice, with a compensation-to-production ratio of 0.36. (The compensation-to-production ratio compares the salary and benefit [compensation] cost to employ a provider with the revenue generated [benefit] for their services.) Compared with a practice employing a full-time physician, a practice employing a full-time PA had an annual financial differential of $52 592 (in 1999 US dollars).16

However, because many PAs and NPs are employed by large capitated managed-care organisations (where all care is prepaid rather than fee-for-service), the economics of their use must be viewed in terms of the resources used for an episode of care rather than the revenue generated. Regarding the benefits of employing PAs, a health maintenance organisation found that when patient variables (age, health status, comorbidities and sex) were held constant, as well as the medical department (general internal medicine, paediatrics, or family medicine), the cost of care by a PA was less than the cost of care by a physician. For some diagnoses, this was due to the lower wage of the PA; in others, it was due to lower use of resources (imaging, laboratory services, medication, referral, and return visit) for the episode of care. Overall, for an episode of acute primary care, the cost of employing a PA was less than the cost of employing a doctor and represented a greater saving to the health maintenance organisation in patient management resources.17

NPs and PAs are cost effective, as they have substantially lower salaries than doctors but see a comparable number of patients per specified period. At certain levels of medical care, when reimbursement is examined, the profits of a health care organisation are increased when a PA or NP provides services. When a national database on group medical practices was assessed, the compensation-to-production ratio was found to be 0.38 for PAs, 0.41 for NPs and 0.49 for family physicians.18

Skill mix

Although the concept of providing a mix of skills from a range of health care personnel in a team-based approach to patient management dates back centuries, the organisation of medicine in the latter quarter of the 20th century led to a wider range of work being delegated to other workers.21 The use of PAs and NPs to deliver health care in areas that are under-served or where physician services are stretched has been the subject of a number of studies. Some of the resulting publications contain useful examples of expanded roles of NPs, PAs and other first-contact personnel from around the globe.22 While it is not clear where in the milieu of medical work PAs and NPs have emerged, it is apparent that their skills largely overlap those of primary care physicians, and that they are also capable of taking on a high degree of responsibility in other areas of medicine.23

The institutional licensure to practise medicine has narrowed the gap between physicians and PAs/NPs, creating more shared dependency (J Strand, J Cawley, E Schneller, Duke University, Durham, NC, USA, personal communication). Non-physician clinicians can bring strengths to different health systems. They are deployed in primary care, emergency departments, hospitals, and in areas with acute shortages and where doctors are overworked. Inner cities tend to welcome any medical personnel resource, especially if they can contribute to the role of diagnosing and treating common problems and providing needed “wellness” checks. General surgery, cardiovascular surgery, orthopaedics and gastroenterology are noted examples where PAs and NPs perform many technical procedures that would be time-consuming for doctors. This division of labour and skill mix frees physicians to manage more patients or oversee more trainees.


The numbers of NPs and PAs in the American medical workforce have increased steadily since 1967. This increase is attributable to a number of factors. First, the medical marketplace has remained strong for the past three decades, resulting in an increase in the number of education programs for both PAs and NPs. However, since the late 1990s, NP education output is declining, while PA education output is increasing. This decline may be related to the overall general shortage of nurses. Given the ageing of the nursing workforce and the waning interest in nursing as a career, the number of NPs entering clinical roles may decrease even further.25

Second, changes in medicine and the health care environment are driving a need for partnership and interprofessional practice. Observers believe that traditional medicine can no longer sustain the old “command and control” model of medical practice (J Strand, J Cawley, E Schneller, Duke University, Durham, NC, USA, personal communication). The intersecting of professions such as the PA/NP–doctor partnership is an example of shared domain and is grounded in the work of Abbott, Freidson and others.26-29 This work emphasises that when a labour shortage occurs, especially in health care, a substitute arises to fill the vacant role.

Third, economics may play a role. According to the Bureau of Labor Statistics, the employment future for PAs and NPs in the US is likely to remain optimistic for the next decade.30 A factor is the 80-hour limit placed on the average working week of medical residents (postgraduate medical trainees) by the Accreditation Council for Graduate Medical Education in 2003. Institutions failing to comply can face loss of accreditation. As a short-term response, many hospitals have employed PAs and NPs to fill staffing gaps.31

With the number of medical students graduating each year largely static, limited growth in residents and fellows (Box), and a decrease in the numbers of international medical graduates both entering and remaining in the US, demand for other health care providers is likely to increase.32 Compound this with an expanding (and ageing) population, declining physician work effort, and a projected decrease in career spans of doctors, nurses and other health professionals, and the problem appears even greater. Newer workforce theories predict that economic expansion correlates with demand for physician services, which places additional pressure on the existing health system, which will only mount as physician supply fails to keep pace.33

Finally, primary care is thought to be in a crisis. Fewer medical school graduates are selecting primary care, and fewer still are remaining in this sector.34-37 With a shortage of physicians interested in general medicine, medical systems are increasingly turning to PAs and NPs to shoulder the burden of primary care. While this may not have been the intent of early policymakers, the reality is that PAs and NPs may be the only resource available in the near future.

  • Roderick S Hooker1

  • Department of Veterans Affairs Medical Service, Dallas VA Medical Center, Dallas, Tex, USA.


Competing interests:

None identified.

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