Search tips
Search criteria 


Logo of nihpaAbout Author manuscriptsSubmit a manuscriptHHS Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
Health Soc Care Community. Author manuscript; available in PMC 2014 January 27.
Published in final edited form as:
PMCID: PMC3903046


Roderick S. Hooker, PhD, MBA, PA1 and Christine M. Everett, MPH, PA, PhD-Candidate2


Shortages of primary care doctors are occurring globally; one means of meeting this demand has been the use of physician assistants (PAs). Introduced in the United States in the late 1960s to address doctor shortages, the PA movement has grown to over 75,000 providers in 2011 and spread to Australia, Canada, Great Britain, The Netherlands, Germany, Ghana, and South Africa. A purposeful literature review was undertaken to assess the contribution of PAs to primary care systems. Contemporary studies suggest that PAs can contribute to the successful attainment of primary care functions, particularly the provision of comprehensive care, accessibility, and accountability. Employing PAs seems a reasonable strategy for providing primary care for diverse populations.

Keywords: Primary Care, Physician Assistant, Collaboration, Teams


We undertook a review about physician assistants (PAs) in primary care - a foundation for understanding how they contribute to the provisions of primary care. The literature is large enough to offer some generalizations, but a secondary goal is to alert the reader to significant gaps in current knowledge. For historical reasons, it is written with an American backdrop but with an eye on the global expansion of PAs and an international readership. Nurse practitioners (NPs) are mentioned when the literature reviewed combines PA/NPs into a single provider category. However, Laurant and colleagues (2009) have extensively reviewed the combined literature on PAs and NPs in a variety of roles and this work will not be repeated here. Instead, this undertaking focuses on useful and contemporary studies to guide employers and policy makers as to whether PAs are suitable providers and how they may best be utilized in primary care.

PAs are recognized as health professionals that practice medicine in collaboration with doctors through delegated clinical tasks and patient management (Cooper 1998, Hooker 2004, Larsson 2002, Lowes 2000, Parle 2006). As of 2011, the US has approximately 75,000 clinically active PAs, and produces approximately 7,000 graduates annually; there are almost 1,000 in four other countries (with substantial growth predicted over the next decade) (Hooker 2010a). Their flexibility and generalist training permits them to function as providers under the supervision of a doctor in a variety of medical specialties and healthcare settings (Hooker 2010b, American Academy of Physician Assistants [AAPA] 2009). One-third (34%) is employed in primary care settings (defined as family medicine, general medicine, and general paediatrics). Because of the uniqueness of the American healthcare system, it is unclear if the benefits experienced from the introduction of PAs as primary care providers will be experienced similarly in other healthcare systems (Hooker 2005). Nor has their use in primary care been consolidated in any systematic fashion that would be useful to potential employers. To address this gap, a review of PAs in primary care was undertaken. A description of PAs in primary care in the U.S. is provided and one question was posed: To what extent do PAs contribute to effective, safe and efficient team-based primary care?

Because of the nature of introducing a new health professional into a doctor-dominated system, policy analysts must assess the performance of PAs in relation to contemporary healthcare delivery. Healthcare organizations interested in evaluations that are not revenue-based are likely to be interested in the effectiveness of PAs. At the heart of the question is identifying the services PAs can perform within the context of a physician-PA primary care team that will be beneficial to the practice, the patient, the employer, and society.


The purpose of this review is to synthesize the available evidence regarding the contribution of PAs to primary care. While the PA profession has been in existence for over 40 years, the empirical study of this profession has been limited and definitive studies that comprehensively evaluate PA contributions to the functions of primary care are lacking. In light of these limitations, a purposeful, policy-relevant review was conducted which categorized the studies based on a generally accepted theoretical model of primary care and relevance to the review question rather than evaluations of study methodology (Gough 2007).

The English language literature for all publications that include PAs in primary care was searched in these citation indices: Google Scholar, PubMed, CINAHL, Medline, Cochrane Database of Systematic Reviews, DARE, Embase, AHRQ, British Library Integrated Catalogue, ProQuest Dissertations and Theses, Sociological Abstracts, World Health Organization (WHO), and Web of Science. Search terms included “physician assistant”, “physician’s assistant,” “Medex,” “physician associate,“ ”primary care,” “family medicine,” and “general practice.” Because PA development during the first two decades was small and the contributions to the literature of marginal value and relevance to contemporary primary care, the search was limited from 1990 through 2010. Studies were included in the review if an observational or experimental design was utilized, primary care physicians and PAs were compared relative to an outcome of interest, and studies were subjected to peer review. Post priori, the studies were sorted into the following areas of interest: description of PAs in primary care (distribution, skills, productivity and role) and contributions to the key functions of primary care (comprehensiveness, coordinated care, continuity of care, accessibility to care, patient-centred), effectiveness, safe care, and efficiency. The majority of the included studies were conducted in the U.S., with 11 undertaken in 4 other countries. Studies excluded were gray literature, editorials, reworked original data, and anecdotal findings.

A total of 93 papers and 1 monograph had comparisons of doctors and PAs in primary care. Primary care was mentioned in each of these papers but sometimes the use was broad and included emerging roles such as hospitalist, oncology, psychiatry, geriatrics, or experiments in healthcare delivery such as telemedicine and retail medicine. When this search was refined, 42 papers and 1 monograph were considered useful to make comparisons between primary care doctors and PAs.

U.S. Physician Assistants in Primary Care

From the beginning of the concept of the PA, and before the term ‘primary care’ was widely used, the PA occupation was created to diagnose and treat common medical conditions in a general practice environment (Jones 2007a, 2007b). It may have been this generalist background that led to their success. The emergence of the PA as an adjunct in delivering primary care services occurred in the early 1980s when the roles between family medicine doctors and PAs became less distinct and primary care more broadly defined (Bodenheimer 2010).

National studies of primary care visits to PAs, NPs, and doctors in the U.S. suggest utility in the public sector, especially in the Department of Veterans Affairs and the Department of Defence, where ratios of PAs to doctors is high (Hooker 2008, Wozniak 1995). Similar ratios of PAs to doctors are not as common across the private sector, although some vertically integrated healthcare systems have staffing ratios of PAs to family practitioners as high as 50% (Hooker 1991). Nationally, the tendency to employ PAs in private practice family and general medicine settings are considerably less than in publically funded Community Health Centers (Hing 2010). Reasons drawing PAs into non-primary care centres on higher remuneration in procedural specialties – surgery, dermatology and emergency medicine lead the list (Morgan 2010).

By the 1990s, evidence had emerged that PAs could expand the delivery of traditional physician-directed services (Osterweis 1993, Schroeder 2002). Consequently, federal policies were enacted to ensure adequate reimbursement for PA services and to encourage employment of PAs in rural underserved areas (Henry 2010). Some of these primary care PAs serve rural and remote populations that could not attract a doctor (Henry 2007).

As of 2011, approximately 75,000 PA are considered clinically active across six countries (Australia, Canada, The Netherlands, South Africa, United Kingdom, and the US). In the US, PA/NPs provide at least 11% of all outpatient medical services. They work in every state and many domains of the federal government (AAPA 2009, Hooker 2008). All of the major medical and surgical specialties employ PAs and their role continues to expand (Morgan 2010). The percent of PAs in primary care has also been undergoing a shift since the mid 1990s due to a number of influences. The most often cited reason is decreasing federal funding for PA education, that at one time emphasized primary care and deployment to underserved areas (Cawley 2008). Other influences include high wage differentials for emergency medicine, dermatology, surgery, and procedure-based roles, along with career dissatisfaction based on long hours, high stress, poor reimbursement, and erosion of scope of practice (Phillips 2009). Approximately 30–40% of clinically active PAs practice in primary care-related specialties (AAPA 2009, Hooker 2008, Hooker 2004).

The Distribution of Physician Assistants in Primary Care

All of the states, four US territories, and four Canadian provinces enable PAs to practice; however, the ratio of PA to population is irregular, and the distribution uneven (Sutton 2010; Jones 2011). Generally speaking, those states/provinces that have high concentrations of universities hosting PA programs have high ratios of PAs, with the Northeastern states having the highest concentration of PAs, PA education programs, and people than the rest of the U.S. (Liang 2010). Five universities in The Netherlands, four in Canada, three in the United Kingdom and one in Australia and Saudi Arabia also educate PAs.

The distribution of PAs also varies by metropolitan status. PAs are more likely to work in urban settings than rural ones; usually the larger the metropolitan area, the greater the concentration of PAs. When non-metropolitan practices are examined, however, the proportion of PAs in rural practice is at least 9%; in some geographical regions such as the far west of the U.S., the ratio of PA/NPs to population is greater than doctors (Grumbach 2003, Pedersen 2008). The vast majority of rural practice PAs are in primary care (AAPA 2009, Henry 2010). Geographical distribution of PAs in other countries is not known.


A national US practice analysis was undertaken in 2004 to assess the knowledge and clinical performance of PAs in practice. Such practice analysis is important to identify the range of skills and the set of beliefs about the domains of knowledge PAs need to possess to be competent in their careers. A total of 5,282 completed surveys and considered representative of the PA population in years of experience, geographical distribution, and practice specialty. The three skills required for most medical encounters were: formulating the most likely diagnosis, basic science concepts, and pharmaceutical therapeutics; it also revealed eight content domains. Overall, survey responses showed few differences in the tasks performed by PAs based on the length of time worked in the profession (Arbett 2009).

Another study described the characteristics of providers, patients, and the type of prescriptions written by PAs and NPs and compared these activities to those in metropolitan and non-metropolitan settings. A PA or NP was the provider of record for 3% of the primary care visits. The three providers wrote prescriptions for 60% of all visits, and the number of prescriptions was 1.3 per visit. PAs were more likely to prescribe a controlled substance than were physicians or NPs. In rural areas, NPs wrote more prescriptions than physicians and PAs, but both appear to prescribe in a manner similar to physicians in the type of medications used in their patient management (Hooker 2005). The majority of PAs in clinical practice appeared to be providing care in a manner similar to each other and similar to what ambulatory care doctors provide.


Analysis of productivity data from a national representative sample showed that, on average over one year, PAs performed 61.4 outpatient visits per week compared with 74.2 visits performed by physicians, for an overall physician full-time equivalent (FTE) estimate of 0.83. However, productivity of PAs varied across practice specialty and location, with generalist PAs providing more visits than their specialist counterparts. Rural productivity was higher than urban, largely due to the concentration of generalist PAs in rural settings (Larson 2001). Additionally, a policy analysis compared the productivity of solo practice physicians who employed PA/NPs with those who did not, demonstrating that solo practice physicians who do employ PA/NPs see an increase in the number of patient visits per week (127.2 vs. 116.4), a decrease in the number of weeks worked per year (47.7 vs. 48.6), and an increase in net income ($220,000 vs. $186,900), despite lower office visit fees ($90 vs. $96.50 for a new patient) (Wozniak 1995).

Additional productivity documentation can be found in a state-level analysis in Utah. Even though PAs make up only 6.3% of the state's combined clinician (physician, PA, NP) workforce, they contribute approximately 7.2% of the patient care full-time equivalents (FTE) in the state. The majority (73%) of Utah PAs works at least 36 hours per week and spends a greater percentage of total hours working in patient care when compared to physicians. The rural PA workforce reported working a greater number of total hours and patient care hours when compared to the overall state-wide PA workforce (Pedersen 2008).

In a Dutch study of a family practice doctor and an American-trained PA, the productivity, based on contacts per 1,000 patients, increased by 17% over one year after the PA was added to a solo practice office. Measured per FTE of a GP, the number of GP contacts decreased slightly (2.3%). Types of contacts, diagnoses, drug prescriptions, and new referrals to primary care of the GPs changed significantly. The number of PA contacts per 1 FTE PA was about 60% of that of the GPs, with clinical activities overlapping substantially. In the aggregate, the PA saw more women, children, and patients aged 25–44 years; performed more practice consultations, made more women’s health-related diagnoses, and prescribed more drugs for dermatological and respiratory problems (Simkens 2009).

Roles of the Physician Assistant in Primary Care

PAs practice collaboratively with physicians to address the health needs of the population served. The role performed by any individual PA is negotiated with the supervising doctor and reflects the experience, training, and preferences of all providers on the team, the needs of the patient population, and the level of trust the physician has with the PA (Jacobson 1998). As a result, there is the potential for significant overlap in the competencies of PAs and doctors. Five cross-sectional studies have compared visits performed by primary care doctors to PAs and NPs using a federal dataset, which demonstrated that, the main reason for a visit and the characteristics of patient seen by doctors and PA/NPs were similar (Aparasu 2001, Genova 2006, Lin 2002, Mills 1998, Mills 2002).

The clinical roles that PAs can perform within the provider team context fall under two broad categories (substitute and complement) and impacts the distribution of patient care among team members (Jacobson 1998, Starfield 1998). In both categories of labour, PAs are providing some form of substitution. When PAs perform all functions of primary care in a manner similar to physicians, they perform substitute roles. According to the philosophical ideal for primary care, this translates into assuming the tangible (the provision of the full complement of primary care services) as well as intangible (patient-provider relationship) attributes of a physician’s professional role for a subset of the patients (i.e., serve as a usual provider of care). One study examined the ability of practice attributes to predict PA performance in a substitute role and found that the most significant correlates included years in practice as a PA, years in practice with the supervising physician, annual income from the practice, practice in a rural county, recognition as the exclusive provider of primary care to patients, and employment in a single-specialty group practice (Chumbler 2001).

PAs can also perform complementary roles in which they substitute for physicians for particular tasks. For example, they may be responsible for providing acute or preventive care to the population served by the provider team. Several studies have highlighted this type of labour for PAs and NPs in the provision of preventive care. A qualitative study that interviewed providers and administrators at nine large healthcare organizations examined the role of NPs and PAs. The researchers found that organizations perceived an important role for NPs and PAs in the delivery of preventive care to women due to women’s preference for female providers, the shortage of female doctors, and the tendency for PA/NPs to place a higher focus on prevention (Coulter 2000). Another study surveyed 1,363 doctors about cancer screening in primary care patients and demonstrated that the majority of those surveyed (73–79% of family physicians and 60–70% of internists) is amenable to PAs providing such examinations. Of these, 631 physicians (46%) reported a PA/NP performing at least one type of cancer-screening examination on their patients, with family physicians more likely than general internists to use PA/NPs to perform cancer-screening examinations. Some evidence suggests that PAs and NPs may perform better at prevention tasks. One retrospective cohort study of 472 patient records that represented 16 million preventive healthcare visits among women ages 50 to 69 years was conducted. The relative risk ratios for breast examination and mammography during preventive visits across provider specialty and training types were compared. Across training degree types, PAs and NPs in primary care are more likely than medical doctors to adhere to cancer screening guidelines (Wallace 2006).

Evidence suggests that PAs can substitute for physicians on a wide range of patient care tasks, supporting the contention that PAs have significant role flexibility (Hooker 2010a, Morgan 2010). However, few empirical studies have evaluated the relationship between the role of the PA within the provider team and outcomes (Richardson 1998, Scheffler 2008).

The Contributions of Physician Assistants to Primary Care


Commonly used measures of comprehensiveness include scope of services provided and rate of referral. Multiple studies have compared the scope of patient care services provided by PAs and physicians in primary care settings and have concluded that PAs can perform 85–90% of services traditionally provided by primary care physicians (Hooker 2010a). Ongoing national surveys of ambulatory medical care delivery systems demonstrate that PAs perform similarly to doctors within visits when types of patients are compared by primary diagnoses. In a study of 1,200 US Community Health Centers, a higher percentage of PA visits were due to an acute condition (48%) compared with physician (34%) and NP visits (33%). Acute conditions were typically injury and illness. Patients with a co-morbid chronic condition made up nearly half of all visits. The most frequent chronic conditions reported were: hypertension, hyperlipidaemia, diabetes, depression, obesity, arthritis, asthma, and chronic and obstructive pulmonary disease. The percent of visits made by patients with any of these specific conditions did not vary by type of clinician. Nor were there differences in percentages of established patients seen by each type of clinician (87–89%). In these federally funded community health centres, which almost exclusively provide primary care, the staffing ratio of PA/NP to doctor averages 30% (range: 0% to 40%) (Hing 2010).

Results from a study in Iowa suggest that comprehensiveness of primary care services varies by geographic location. Findings indicated that rural primary care providers performed more procedures than their metropolitan counterparts. Among 55 responding PAs, all reported patient education, prescribing, interpreting radiographs, referring patients, and providing a wide range of services similar to their physician counterparts. Few differences emerged when comparing family medicine doctors to PAs in rural areas, suggesting that both clinicians are providing a broad array of medical services (Dehn 1999).

Five studies on referral rates and patterns by PAs in primary care indicate that referring is an activity that does not substantially differ between PAs and doctors (Enns 2003, Hooker 2004, Kimball 2008, Rubenstein 2007, Simkens 2009).

Coordinated Care

Care is coordinated when patients receive appropriate care in a cost-effective manner (Scheffler 1996). Many conceptualizations of care coordination exist, but all agree that communication between primary care practitioners, other healthcare professionals, and patients is a key component of coordination (Bodenheimer 2010, Starfield 1998, Stille 2005). Coordination of care is generally viewed by primary care PAs as a function that falls within their clinical role (Jacobson 1998). Specialist physicians report willingness to accept patient referrals from primary care PAs and general satisfaction with the appropriateness and timeliness of the referrals (Enns 2003, Hooker 2004, Kimball 2008, Rubenstein 2007; Simkens 2009).

Continuity of Care

Continuity of care can refer to the transfer of information between episodes of care (informational continuity) or the provision of care over time by consistent providers (longitudinally and/or relational continuity) (Cabana 2004, Donaldson 1996c; Haggerty 2003). A patient-clinician relationship is a central feature of primary care; the potential for decreased relationship exists when a provider team approach is implemented. Two studies have evaluated the relationship between continuity and quality of care using a cross-sectional analysis of patient surveys. One evaluated the effects of visit continuity for patients (N=14,835) of a large multi-specialty practice served by primary care provider teams with PAs or NPs, and the patient perceptions of the quality of primary care. Patients who only saw their primary care physician reported significantly higher physician-patient relationship quality, and better assessments of organizational features of care (such as access and integration of care) than visits with providers other than their primary care physician. However, patients who had visits only with providers on their primary care team had significantly higher assessments of the clinical team, but lower assessments of their physician’s knowledge of them as a person than did those who had visits with providers off the team. The subgroup of patients that experienced visits with their primary care PA or NP team members reported better primary care experiences (Rodriguez 2007).

Another survey of attendees of primary care clinics at five Department of Veterans Affairs medical centres (N=21,689) evaluated the extent to which self-reported continuity of care related to patient satisfaction after adjusting for patient, provider, and clinic characteristics. The mean adjusted humanistic score for patients who reported always seeing the same provider was 17.3 points higher than for those who rarely saw the same provider. Similarly, the mean adjusted organizational score was 16.3 points higher for patients who always saw the same provider compared to those who rarely saw the same provider. Demographic factors, socioeconomic status, health status, clinic site, and patient utilization of services were all associated with both the adjusted humanistic and organizational scores of the scale. There were no differences in type of provider (PA/NPs or doctors) when distinguished by the patient suggesting it was continuity of care, and not necessarily the type of provider, that was associated with higher patient satisfaction (Fan 2005).

Accessibility to Care

Accessible care is care that is easy for patients to obtain in a timely fashion (Donaldson 1996a). Empirical evidence suggests that PAs can improve access to care to underserved patients and open access practices. The primary care patients of PAs, rather than doctors, are slightly more likely to be female, rural, uninsured, or publicly insured. One study utilized administrative data and surveyed primary care clinicians including doctors, NPs, PAs, and midwives in California and Washington to determine if practice in underserved areas varied by provider type. PAs demonstrated a greater proclivity for providing care to the underserved as they ranked first or second in both states as the providers with the highest proportion of members practicing in rural areas, health professional shortage areas, and vulnerable population areas (Grumbach 2003). The finding that PAs practice in greater proportion than physicians and nurses in areas of low population density (i.e., rural areas) has also been identified in studies in Iowa and Utah (Dehn 1999, Pedersen 2008).

When compared to patients reporting primary care doctors as a usual source of care, patients of PAs were more likely to live in rural areas, lack insurance or have public insurance other than Medicare, report lower perceived access to care, and/or have decreased likelihood of having some preventive care such as comprehensive health exam or mammograms. Despite these differences in characteristics and utilization, there were no differences in patient complexity or in self-rated health between primary care patients of physicians and PAs, suggesting PAs can provide access to a usual source of care for a broad range of patients (Everett 2009).

Appointment delays impede access to primary healthcare, and open access (OA) scheduling may improve the quality of primary healthcare. A study assessed whether implementing OA during a 12-month period impacted practice and patient outcomes and differed by provider type. Providers (doctors, PAs, and NPs) in four practices successfully implemented OA. On average, providers reduced their delay to the next available preventive care appointment from 36 to 4 days. No-show rates declined and overall patient satisfaction improved 16%. Continuity of care followed a similar pattern of improvement. Staff satisfaction neither improved nor declined. No significant differences in outcomes were seen by provider type suggesting that PAs and doctors are similar in their adaptability to complex organizational changes aimed at improving access (Bundy 2005).

Patient-Cantered Care

Patient-centred care is recognized as a critical function of primary care, but agreement of the definition of this function is lacking. Most studies that have evaluated patient-centred care include patient satisfaction as an outcome (Mead 2002). Satisfying care, in this regard, means the patient completes the visit feeling their needs were met. No amount of quality care by the PA will overcome the stigma of unsatisfactory care if that is the way the patient perceives it.

To assess the extent to which the experiences of patients vary according to type of primary care provider (PA, NP, or doctor), a national, cross-sectional survey of elderly patients receiving U.S. government health insurance (Medicare) was undertaken. The beneficiaries completing the survey identified a primary care provider and recorded satisfaction data, patient socio-demographic characteristics, healthcare experience, types of care, and types of supplemental insurance. A total of 146,880 completed surveys were analysed. While a small number (3,770 or 2.8%) of respondents identified a PA or an NP as their sole personal provider, for questions on satisfaction with their personal care clinician, results were similar across the three providers. Patients who reported a physician as their primary care provider were more likely to have supplemental insurance as compared with patients who reported receiving care from a PA or NP. The conclusion was that Medicare beneficiaries are generally satisfied with their medical care and do not distinguish preferences based on type of provider. For this group, the patient viewed all clinicians in primary care similarly across all patient characteristics (Hooker 2005).

Effective Care

Effectiveness of primary care delivery may depend, at least in part, on using the correct mix of personnel. Starfield (1993) showed that the division of labour and economy of scale maximizes the clinical capabilities of healthcare professionals. In primary care practice, it is neither necessary nor particularly efficient for each patient to be seen by a physician. Since PAs are, by definition, physician-supervised clinicians, the very nature of their clinical role is to work with doctors in collaborative provider teams. To be effective, the PA needs to provide quality care to similar patients for similar diagnoses that result in outcomes comparable to those of a doctor. Several studies have been conducted which compare the care provided by PAs and doctors on quality measures including processes of care and/or patient outcomes for specific diagnoses.

Back pain

In an effort to improve the cost-effectiveness of primary care for low-back pain, an in-clinic education intervention program was designed to provide family practice doctors and PAs with specific information, tools, and techniques that the literature suggested should be associated with more satisfying and cost-effective care. The back pain-related beliefs, attitudes, and behaviours of 15 primary care providers in a large health maintenance organization (HMO) clinic and of 14 family physicians in six group practices were assessed before and after the intervention. Significant increases were noted in the proportions of providers who felt confident they knew how to manage low-back pain, who believed their patients were satisfied, and who claimed they reassured patients that they did not have serious disease (whether they were PAs or doctors) (Bush 1993).


PAs and NPs are primary care providers for patients with HIV in some clinics, but little is known about the quality of care they provide. A cross-sectional analysis compared eight quality-of-care measures assessed by medical record review. The quality of care provided by PA/NPs was compared with that provided by physicians in 68 HIV care sites. The authors surveyed 243 clinicians (177 physicians and 66 NP/PAs) and reviewed medical records of 6,651 persons with HIV or AIDS. After adjustments for patient characteristics, most of the quality measures did not differ between NPs and PAs (and did not differ when compared to infectious disease specialists or generalist HIV experts). Adjusted rates of purified protein derivative (PPD) testing and Papanicolaou cervical screens were higher for NPs and PAs (0.63 and 0.71, respectively) than for infectious disease specialists (0.53) or generalist HIV experts (0.47). PAs and NPs had higher performance scores than generalist non–HIV experts on six of the eight quality measures. The authors concluded that for the measures examined, the quality of HIV care provided by PA/NPs was similar to that of physician HIV experts and generally better than physicians (non–HIV experts). Preconditions for this level of performance included high levels of experience, focus on a single condition, participation in teams, and easy access to clinicians with HIV expertise (Wilson 2005).

Metabolic diseases

Three studies have evaluated the relationship between the type of provider and the attainment of treatment goals for diabetes, dyslipidaemia, and hypertension. One cross-sectional analysis of 19,660 patients with diabetes, coronary artery disease, or hypertension was conducted in the VA Connecticut Health Care System. While significant differences were seen in the type of patients cared for by PA/NPs and resident physicians, attainment of goals for each condition was similar, with one exception; PA/NPs were more likely than resident physicians to attain an HgbA1c goal of less than 7.5 (Federman 2005). Another cross-sectional study of 46 family medicine practices measured adherence to American Diabetes Association guidelines via chart audits of 846 patients with diabetes. Compared with practices employing PAs, practices employing NPs were more likely to measure haemoglobin A1c (HgbA1c) levels (66% vs. 33%), lipid levels (80% vs. 58%), and urinary micro albumin levels (32% vs. 6%); and to have treated for high lipid levels (77% vs. 56%). Practices with NPs were more likely than physician-only practices to assess HgbA1c levels (66% vs. 49%) and lipid levels (80% vs. 68%). However, these process improvements did not translate into improved outcomes, with the exception of better attainment of lipid targets in practices employing NPs. These effects could not be attributed to use of diabetes registries, health risk assessments, nurses for counselling, or patient reminder systems. Those practices employing either PAs or NPs were perceived as busier and had larger total staffs than physician-only practices. With regard to diabetes process measures in this study, family practices employing NPs performed better than those with physicians only, and with those employing PAs (Ohman-Strickland 2008). Similarly, a cohort study conducted on 88,682 primary care patients in 198 Veterans Administration clinics demonstrated that clinics that included NPs were associated with lower HbA1Cs (approximately 0.31 percentage points) and clinics with PAs did not show a statistically significant difference in HbA1C when compared to clinics without PAs or NPs (Jackson 2010).

Common Geriatric Conditions

A randomized trial assessed the impact of a PA case manager responsible for screening; case finding and referral of geriatric primary care patients for common geriatric conditions (n=792). Despite finding no difference in functional outcomes or hospital utilization, patients who were provided with a PA case manager were morel likely to have the target conditions identified (depression, cognitive and functional impairment, falls, and urinary incontinence) than patients receiving standard care (Rubenstein 2007). The findings suggest that incorporating PAs in supplemental roles for target populations can increase case finding, assessment, and referral for previously under-diagnosed and treated conditions.

Parkinson’s disease

A study compared PA, NP, and physician knowledge of the pharmacological management of Parkinson's disease (PD) and their preferences for referring PD patients to specialists. PA/NPs answered 46% and physicians answered 50% of questions about PD pharmacotherapy, in agreement with recommended clinical practice (P = 0.14). None of the providers differed in their preference to refer a PD patient to a specialist for management, but PAs and NPs were more likely to refer a patient to a specialist for diagnostic confirmation. The authors concluded that given trends for more PA and NP autonomy in patient care, it was reassuring that all providers had similar knowledge of PD pharmacotherapy. They also added that policies to substitute PAs and NPs for physicians might increase referrals to specialty providers for diagnostic confirmation (Swarztrauber 2007).

Safe Care

The results of the inputs and throughputs of care are critical, but if outcomes are unfavourable, the PA will be viewed as less effective than the doctor. The examination of differences in liability among professions is one way to assess safety of care provided by healthcare professionals. A study assessing whether PA and NP utilization increased liability analysed the malpractice incidence, payment amount and other measures of liability among doctors, PAs and advanced practice nurses (APNs). From 1991 through 2007, 324,285 entries were logged involving 273,693 providers of interest. Significant differences in liability reports were found among doctors, PAs, and APNs. Physicians made, on average, malpractice payments twice that of PAs, but less than that of APNs. The probability of making a malpractice payment was 12 times less for PAs and 24 times less for APNs than physicians during the study period. For all three providers, missed diagnosis was the leading reason for a malpractice report; female providers incurred higher payments than males. Trend analysis suggests that the rate of malpractice payments for physicians, PAs, and APNs has been steady and consistent with the growth in the number of providers. There were no observations or trends to suggest that PAs and APNs increase liability. From a policy standpoint, it appears that the incorporation of PAs and APNs into American society has been a safe undertaking, at least when compared to doctors (Hooker 2009).

Efficiency: Cost Beneficial Use of PAs in Primary Care

One analysis focused on whether PAs were cost-beneficial to employers. PAs and physicians within a large HMO saw four common acute medical conditions over one year. An episode approach was undertaken to identify all institutional resources used for a condition and 12,700 medical office visits were analysed for each type of provider. Patient characteristics were controlled for age, gender, and health status. A multivariate analysis identified significant cost differences in each cohort of patients. In every condition managed by PAs, the total cost of the visit was less than that of a physician in the same department. In no instance was a PA statistically different from physicians in use of laboratory and imaging costs and, in each instance; the total cost of the episode was less when treated by a PA. In some instances, PAs ordered fewer laboratory tests than physicians for the same episode of care. There were no differences in the rate of return visits for a diagnosis. When the type of provider encounters were further delineated by departments of family medicine, general internal medicine, and paediatrics, the results remained the same. These findings suggest that PAs are not only cost effective from a labour standpoint but are also cost-beneficial to employers. In most cases, they order resources for diagnoses and treatment in a manner similar to physicians for an episode of care, but the cost of an episode of an illness is more economical overall when the PA delivers the care, which can be explained in part by the PA’s lower salary (Hooker 2002).

To estimate the savings in labour costs that might be realized per primary care visit from increased use of PAs and NPs in primary care, the practices of another HMO were examined; 26 primary care practices and data on approximately two million visits delivered by 206 practitioners were extracted from computerized visit records. On average, PA/NPs provided one in three adult medicine visits and one in five paediatric medicine visits. Likelihood of a PA/NP visit was significantly higher than average among patients presenting with minor acute illness (e.g., acute pharyngitis). In adult medicine, the likelihood of a PA/NP visit was lower than average among older patients. Practitioner labour costs per visit (and total labour costs per visit) were lower among practice arrangements with greater use of PA/NPs, standardized for case mix. The authors concluded that primary care practices that used more PA/NPs in care delivery realized lower practitioner costs per visit than practices that used fewer PA/NPs (Roblin 2004).


The literature regarding PAs in team-based primary care, spanning 1990 through 2010, demonstrates that these providers have enhanced certain aspects of the delivery of primary care. One of the attributes is that PAs have significant role flexibility, allowing healthcare systems multiple options for incorporating PAs into primary care provider teams. Evidence to date suggests that PAs can make significant contributions to select functions of primary care. These clinicians have also demonstrated inclination to provide care to underserved populations, thereby improving access to primary care. Available evidence suggests that the care provided by PAs is safe, effective and satisfying to patients insofar as it is comparable to doctors. Provision of care by PAs has a favourable cost benefit, thereby improving efficiency. The strength of this undertaking is that it identifies work where PAs are both cost effective and complementary with primary care doctors in attaining the functions of primary care.


This study identifies where and how PAs can be utilized in primary care and at the same time demonstrates that the literature is far from complete. While the research conducted on PAs in primary care suggests their utilization is favourable, all included studies had less than optimal scope and sample, limiting our capacity to make definitive statements about PAs in primary care. Significant work remains to be completed before we can claim to have a reasonable understanding of the scope of PA contributions to primary care.

Three broad areas of research are critical to optimizing the contribution of PAs to primary care: role delineation, team processes, and patient outcomes. Current theories regarding roles of PAs in primary care have face validity, but the impact of these roles will not be understood until the theories are operational and empirically studied. Qualitative studies on team member perceptions of PA roles could assist in this endeavour. Understanding how roles impact team processes such as the provision of coordinated care and communication between team members is also critical. The literature on PAs in primary care is lopsided towards the U.S. thus inhibiting international generalizations. Finally, evaluations of the impact of PA care on patient outcomes, particularly for chronic illness, are essential to understanding the full capacity of PAs to contribute to the delivery of team-based primary care.


Primary care is a bedrock principal in meeting the needs of society by providing integrated, accessible, and accountable care. Current evidence suggests that the PA has surfaced as a valuable contributor to this important mission, and is well suited to the provision of integrated care within provider teams in a variety of settings. The generalist training of the profession allows for overlapping competency with primary care doctors and has been critical aspect of its adaptability. Access to safe and effective care is enhanced when PAs are part of the primary care provider team, and some patients will preferentially select them. These observations stand up to scrutiny and suggest that PAs are cost effective to employers and probably cost beneficial to institutions. However, limited empirical research has been undertaken comparing the process and the patient outcomes of coordination when performed by primary care PAs-doctor teams.

Since the maximum substitution model of incorporating PAs in primary care was proposed by Record (1981), a number of policies have been enacted that not only permit the PA to work but to thrive. These primary care policies are being played out in a growing number of countries (Ashton 2007; Farmer 2009; Jolly 2008; Mullan 2007; Simkens 2009). As demand for care rises and the supply of doctors fails to keep pace, the need for more primary care PAs will increase. Sustainability of any medical system involves organizational challenges and novel solutions. PAs may be one tool for meeting those challenges.


  • PAs function under doctor supervision
  • The generalist training of PAs permits widespread use in most areas of medicine
  • PAs are educated in the physician model of medicine


  • The contributions of PAs to primary care involve effectiveness, safety, patient satisfaction, and outcomes of care comparable to a physician.
  • The addition of PAs to primary care teams tends to improve care that is coordinated, comprehensive and helps to maintain continuity of care.
  • Role delineation of PAs in primary care appears to be underdeveloped.



CME received financial support from:

AHRQ National Research Service Award (T32 HS00083); Community-Academic Partnerships core of the University of Wisconsin Institute for Clinical and Translational Research (UL1RR025011); Health Innovation Program


  • American Academy of Physician Assistants (AAPA) AAPA Physician Assistant Census Report. Alexandria, VA: American Academy of Physician Assistants; 2009.
  • Aparasu RR, Hegge M. Autonomous ambulatory care by nurse practitioners and physician assistants in office-based settings. Journal of Allied Health. 2001;30(3):153–159. [PubMed]
  • Arbett S, Lathrop J, Hooker RS. Using practice analysis to improve the certifying examinations for PAs. Journal of the American Academy of Physician Assistants. 2009;22(2):31–36. [PubMed]
  • Ashton CW, Aiken A, Duffie D. Physician Assistants--a solution to wait times in Canada? Healthcare Management Forum / Forum Gestion Des Soins De Santé 2007;20(2):38–42. [PubMed]
  • Bodenheimer T, Pham HH. Primary care: current problems and proposed solutions. Health Affairs. 2010;29(5):799–805. [PubMed]
  • Buchan J, O'may F, Ball J. New role, new country: introducing US physician assistants to Scotland. Human Resources for Health. 2007;5(4):13. [PMC free article] [PubMed]
  • Bundy DG, Randolph GD, Murray M, Anderson J, Margolis PA. Open access in primary care: results of a North Carolina pilot project. Pediatrics. 2005;116(1):82–88. [PubMed]
  • Bush T, Cherkin D, Barlow W. The impact of physician attitudes on patient satisfaction with care for low back pain. Archives of Family Medicine. 1993;2(3):301–305. [PubMed]
  • Cabana MD, Jee SH. Does continuity of care improve patient outcomes? Journal of Family Practice. 2004;53(12):974–980. [PubMed]
  • Cawley JF. Physician assistant and Title VII support. Academic Medicine. 2008;83(11):1049–1056. [PubMed]
  • Cawley JF, Hooker RS. Physician assistants: does the US experience have anything to offer other countries? Journal Health Services Research & Policy. 2003;8(2):65–67. [PubMed]
  • Cawley JF, Hooker RS. A brief overview of physician assistants in the United States. The Advisor: The Journal of the National Association of Advisors for the Health Profession. 2005;25(2):6–10.
  • Centre for Review and Dissemination. Systematic reviews: CRD’s guidance for undertaking reviews in health care. York: University of York; 2009.
  • Chumbler NR, Weier AW, Geller JM. Practice autonomy among primary care physician assistants: the predictive abilities of selected practice attributes. Journal of Allied Health. 2001;30(1):2–10. [PubMed]
  • Cooper RA, Henderson T, Dietrich CL. Roles of nonphysician clinicians as autonomous providers of patient care [see comments] Journal of the American Medical Association. 1998;280(9):795–802. [PubMed]
  • Coulter I, Jacobson P, Parker LE. Sharing the mantle of primary female care: physicians, nurse practitioners, and physician assistants. Journal of the American Medical Womens Association. 2000;55(2):100–103. [PubMed]
  • Dehn RW, Hooker RS. Implications for practice and education. Clinical activities of Iowa family practice physician assistants. Journal of the American Academy of Physician Assistants. 1999;12(4):63–74. [PubMed]
  • Donaldson MA, Yordy KD, Lohr KN, Vanselow NA, Alpert JJ, Boykins CY, Brown CV, Cameron K, Duarte PT, Ellsworth P, Garrison RS, Green LA, Griner PF, Johnson J, Jones PE, Lamberts H, Nannis PW, Palmer RH, Ross-Lee B, Ryan SA, Scheffler RM, Winters WL. Defining Primary Care. Washington, DC: National Academy Press; 1996a.
  • Donaldson MA, Yordy KD, Lohr KN, Vanselow NA, Alpert JJ, Boykins CY, Brown CV, Cameron K, Duarte PT, Ellsworth P, Garrison RS, Green LA, Griner PF, Johnson J, Jones PE, Lamberts H, Nannis PW, Palmer RH, Ross-Lee B, Ryan SA, Scheffler RM, Winters WL. The Delivery of Primary Care. Washington, DC: National Academy Press; 1996b.
  • Donaldson MA, Yordy KD, Lohr KN, Vanselow NA, Alpert JJ, Boykins CY, Brown CV, Cameron K, Duarte PT, Ellsworth P, Garrison RS, Green LA, Griner PF, Johnson J, Jones PE, Lamberts H, Nannis PW, Palmer RH, Ross-Lee B, Ryan SA, Scheffler RM, Winters WL. The Nature of Primary Care. Washington, DC: National Academy Press: 1996c.
  • Donaldson MA, Yordy KD, Lohr KN, Vanselow NA, Alpert JJ, Boykins CY, Brown CV, Cameron K, Duarte PT, Ellsworth P, Garrison RS, Green LA, Griner PF, Johnson J, Jones PE, Lamberts H, Nannis PW, Palmer RH, Ross-Lee B, Ryan SA, Scheffler RM, Winters WL. Primary Care: America's Health in a New Era. Washington, DC: National Academy Press; 1996d.
  • Enns SM, Wynn T, Muma RD, Lary MJ. Examining attitudes of specialist physicians regarding physician assistant referrals. Journal of Allied Health. 2003;32(4):270–274. [PubMed]
  • Everett CM, Schumacher JR, Wright A, Smith MA. Physician assistants and nurse practitioners as a usual source of care. Journal of Rural Health. 2009;25(4):407–414. [PMC free article] [PubMed]
  • Fan VS, Burman M, McDonell MB, Fihn SD. Continuity of care and other determinants of patient satisfaction with primary care. Journal of General Internal Medicine. 2005;20(3):226–233. [PMC free article] [PubMed]
  • Farmer J, Currie M, West C, Hyman J, Arnott N. Evaluation of Physician Assistants to NHS Scotland: Final Report. Edinburgh: Scotland NHS; 2009.
  • Genova NJ. Paying for performance: an American PA in Britain and the NHS Quality Outcome Framework. Journal of the American Academy of Physician Assistants. 2006;19(6):25, 6, 52. [PubMed]
  • Grumbach K, Hart LG, Mertz E, Coffman J, Palazzo L. Who is caring for the underserved? A comparison of primary care physicians and nonphysician clinicians in California and Washington. Annals of Family Medicine. 2003;1(2):97–104. [PubMed]
  • Haggerty JL, Reid RJ, Freeman GK, Starfield BH, Adair CE, McKendry R. Continuity of care: a multidisciplinary review. British Medical Journal. 2003;327(7425):1219–1221. [PMC free article] [PubMed]
  • Henry L, Hooker RS, Yates K. The role of the physician assistant in rural health: a systematic review of the literature. Journal of Rural Health. 2010;26(4)
  • Henry LR, Hooker RS. Retention of physician assistants in rural health clinics. Journal of Rural Health. 2007;23(3):207–214. [PubMed]
  • Hing E, Hooker RS, Ashman J. Primary health care delivery in Community Health Centers. Annals of Family Medicine. 2010 [in review]
  • Hooker RS. Medical care utilization: MD-PA/NP comparisons in an HMO. New York: Praeger; 1986.
  • Hooker RS. A cost analysis of physician assistants in primary care. Journal of the American Academy of Physician Assistants. 2002;15(11):39–48. [PubMed]
  • Hooker RS. Physician assistants in occupational medicine: how do they compare to occupational physicians? Occupational Medicine (Oxford, England) 2004;54(3):153–158. [PubMed]
  • Hooker RS. Federally employed physician assistants. Military Medicine. 2008;173(9):895–899. [PubMed]
  • Hooker RS. The future of the physician assistant movement. Medical Journal of Australia. 2010a;192(3):116. [PubMed]
  • Hooker RS, Carter R, Cawley JF. The National Commission on Certification of Physician Assistants: history and role. Perspective on Physician Assistant Education. 2004;15(1):8–15.
  • Hooker RS, Cawley JF. The hidden rheumatology workforce. Arthritis Practitioner. 2005;1(3):34.
  • Hooker RS, Cawley JF, Leinweber W. Career flexibility of physician assistants and the potential for more primary care. Health Affairs. 2010b;29(5):880–886. [PubMed]
  • Hooker RS, Cipher DJ. Physician assistant and nurse practitioner prescribing: 1997–2002. Journal of Rural Health. 2005;21(4):355–360. [PubMed]
  • Hooker RS, Cipher DJ, Sekscenski E. Patient satisfaction with physician assistant, nurse practitioner, and physician care: a national survey of Medicare beneficiaries. Journal of Clinical Outcomes Management. 2005;12(2):88–92.
  • Hooker RS, Freeborn DK. Use of physician assistants in a managed health care system. Public Health Reports. 1991;106(1):90–94. [PMC free article] [PubMed]
  • Hooker RS, Hogan K, Leeker E. The globalization of the physician assistant profession. Journal of Physician Assistant Education. 2007;18(3):76–85.
  • Hooker RS, Kole L. Physician assistants in a changing world [editorial] Journal of the American Academy of Physician Assistants. 2002;15(10):4, 32. [PubMed]
  • Hooker RS, MacDonald K, Patterson R. Physician assistants in the Canadian Forces. Military Medicine. 2003;168(11):948–950. [PubMed]
  • Hooker RS, Nicholson J, Le T. Does the employment of physician assistants and nurse practitioners increase liability? Journal of Medical Licensure and Discipline. 2009;95(2):6–16.
  • Hooker RS, Cawley JF, Asprey DP. Physician Assistant: Policy and Practice, 3e. Philadelphia, Pa.: F.A.Davis; 2010b.
  • Hooker RS, Kuilman L. Physician assistant education: five countries. Journal of Physician Assistant Education. 2011;22(1):53–58. [PubMed]
  • Hutchinson L, Marks T, Pittilo M. The physician assistant: would the US model meet the needs of the NHS? BMJ. 2001;323(7323):1244–1247. [PMC free article] [PubMed]
  • Jacobson PD, Parker LE, Coulter ID. Nurse practitioners and physician assistants as primary care providers in institutional settings. Inquiry. 1998;35(4):432–446. [PubMed]
  • Jolly R. Health Workforce: A Case for Physician Assistants? Canberra, Australia: Parliamentary Library; 2008.
  • Jones PE. Forty years and counting: the past, present, and future of physician assistant education. Journal of Physician Assistant Education. 2007a;18(3):4–5.
  • Jones PE. Physician assistant education in the United States. Academic Medicine. 2007b;82(9):882–887. [PubMed]
  • Jones I, Hooker RS. Physician assistants in Canada: a health policy initiative. Canadian Family Physician. 2011;57:e83–e88. [PMC free article] [PubMed]
  • Kimball BA, Rothwell WS. Physician assistant practice in Minnesota; providing care as part of a physician-directed team. Minnesota Medicine. 2008;91(5):45–48. [PubMed]
  • Larson EH, Hart LG, Ballweg RM. National estimates of physician assistant productivity. Journal of Allied Health. 2001;30(3):146–152. [PubMed]
  • Larsson LS, Zulkowski K. Utilization and scope of practice of nurse practitioners and physician assistants in Montana. Journal of the American Academy of Nurse Practitioners. 2002;14(4):185. [PubMed]
  • Laurant M, Harmsen M, Wollersheim H, Grol R, Faber M, Sibbald B. The impact of nonphysician clinicians: do they improve the quality and cost-effectiveness of health care services? Medical Care Research and Review. 2009;66(6 Suppl):36S–89S. [PubMed]
  • Liang M. Twenty-Fifth Annual Report on Physician Assistant Educational Programs in the United States, 2008–2009. Alexandria, VA: Physician Assistant Education Association; 2010.
  • Lin SX, Hooker RS, Lenz ER, Hopkins SC. Nurse practitioners and physician assistants in hospital outpatient departments, 1997–1999. Nursing Economics. 2002;20(4):174–179. [PubMed]
  • Liu C, Chien C, Chou P, Liu J, Chen VT, Wei J, Kuo Y, Lang H. An analysis of job satisfaction among physician assistants in Taiwan. Health Policy. 2005;73(1):66–77. [PubMed]
  • Lowes R. What do PA, NP, and CNM spell? A revolution in health care. Medical Economics. 2000;77(6):156, 8, 161–163. [PubMed]
  • Mead N, Bower P. Patient-centred consultations and outcomes in primary care: a review of the literature. Patient Education Counselling. 2002;48(1):51–61. [PubMed]
  • Mills AC, McSweeney M. Nurse practitioners and physician assistants revisited: do their practice patterns differ in ambulatory care? Journal of Professional Nursing: Official. Journal of the American Association of Colleges of Nursing. 2002;18(1):36–46. [PubMed]
  • Mills AC, McSweeney M, Lavin MA. Characteristics of patient visits to nurse practitioners and physician assistants in hospital outpatient departments. Journal of Professional Nursing: Official Journal of the American Association of Colleges of Nursing. 1998;14(6):335–343. [PubMed]
  • Mittman D, Cawley JF, Fenn WH. Physician assistants in the United States. BMJ. 2002;325:485–487. [PMC free article] [PubMed]
  • Moore GT. Will the power of the marketplace produce the workforce we need? Inquiry. 1994;31(3):276–282. [PubMed]
  • Morgan PA, Hooker RS. Choice of specialty among physician assistants in the United States. Health Affairs. 2010;29(5):887–891. [PubMed]
  • Mullan F, Frehywot S. Non-physician clinicians in 47 sub-Saharan African countries. Lancet. 2007;370(9605):2158–2163. [PubMed]
  • Nelson LB. New Jersey physician assistant graduates are successful practitioners. The. Journal of the Medical Society of New Jersey. 1982;79(11):829–833. [PubMed]
  • Ohman-Strickland PA, Orzano AJ, Solberg LI, DiCiccio-Bloom B, O’Malley D, Tallia AF, Balasubramanian BA, Crabtree BF. Quality of diabetes care in family medicine practices: influence of nurse-practitioners and physician’s assistants. Annals of Family Medicine. 2008;6(1):14–22. [PubMed]
  • Osterweis M, Garfinkel S, editors. Roles and Functions of Non-Physician Practitioners in Primary Care. Washington, DC: The Association of Academic Health Centers; 1993.
  • Parle JV, Ross NM, Doe WF. The medical care practitioner: developing a physician assistant equivalent for the United Kingdom. Medical Journal of Australia. 2006;185(1):13–17. [PubMed]
  • Pedersen DM, Chappell B, Elison G, Bunnell R. The productivity of PAs, APRNs, and physicians in Utah. Journal of The American Academy of Physician Assistants. 2008;21(1):42–47. [PubMed]
  • Petticrew M, Robers H. Systematic Reviews in the Social Sciences: A Practical Guide. Malden, MA: Blackwell Publishing; 2006.
  • Phillips RL, Dodoo MS, Petterson S, Bazemore A, Teevan B, Bennett K, Legagneur C, Rudd J, Philips J. Specialty and geographic distribution of the physician workforce: What influences medical student and resident choices? Washington, DC: Robert Graham Center; 2009.
  • Record JC. Staffing Primary Care in 1990: Physician Replacement and Cost Savings. 1981
  • Record JC, Blomquist RH, McCabe MA, McCally M, Berger BD. Delegation in adult primary care: the generalizability of HMO data. In Record, J.C. 1981. Staffing Primary Care in 1990: Physician Replacement and Cost Savings. Springer Series on Health Care & Society. 1981;6:68–83. [PubMed]
  • Repicky PA, Mendenhall RC, Neville RE. The professional role of physician's assistants in adult ambulatory care practices. Evaluation & the Health Professions. 1982;5(3):283–301. [PubMed]
  • Richardson G, Maynard A, Cullum N, Kindig D. Skill mix changes: substitution or service development? Health Policy. 1998;45(2):119–132. [PubMed]
  • Roblin DW, Howard DH, Becker ER, Adams EK, Roberts MH. Use of midlevel practitioners to achieve labor cost savings in the primary care practice of an MCO. Health Services Research. 2004;39(3):607–626. [PMC free article] [PubMed]
  • Rodriguez HP, Rogers WH, Marshall RE, Safran DG. Multidisciplinary primary care teams: effects on the quality of clinician-patient interactions and organizational features of care. Medical Care. 2007;45(1):19–27. [PubMed]
  • Rubenstein LZ, Alessi CA, Josephson KR, Trinidad Hoyl M, Harker JO, Pietruszka FM. A randomized trial of a screening, case finding, and referral system for older veterans in primary care. Journal of the American Geriatrics Society. 2007;55(2):166–174. [PubMed]
  • Scheffler RM, Waitzman NJ, Hillman JM. The productivity of physician assistants and nurse practitioners and health work force policy in the era of managed health care. Journal of Allied Health. 1996;25(3):207–217. [PubMed]
  • Scheffler RM. Is There a Doctor in the House? Market Signals and Tomorrow's Supply of Doctors. San Francisco, CA: Stanford University Press; 2008.
  • Schroeder SA. Primary care at a crossroads. Academic Medicine. 2002;77(8):767–773. [PubMed]
  • Simkens ABM, van Baar ME, van Balen FAM, Verheij RA, van den Hoogen HJM, Schrijvers AJP. The physician assistant in general practice in the Netherlands. Journal of Physician Assistant Education. 2009;20(1):30–38.
  • Starfield B. Primary Care: Balancing Health Needs, Services, and Technology. Oxford University Press, USA; 1998.
  • Starfield BH. Roles and functions of non-physician practitioners in primary care. Washington, DC: The Association of Academic Health Centers; 1993. In Osterwise et al.
  • Steinwachs DM, Weiner JP, Shapiro S, Batalden P, Coltin K, Wasserman F. A comparison of the requirements for primary care physicians in HMOs with projections made by the GMENAC. New England Journal of Medicine. 1986;314(4):217–222. [PubMed]
  • Stille CJ, Jerant A, Bell D, Meltzer D, Elmore JG. Coordinating care across diseases, settings, and clinicians: a key role for the generalist in practice. Annals of Internal Medicine. 2005;142(8):700–708. [PubMed]
  • Sutton JP, Ramos C, Lucado J. US physician assistant (PA) supply by state and county in 2009. Journal of the American Academy of Physician Assistants. 2010;23(9):E2–E8.
  • Swarztrauber K, Graf E. Nonphysicians' and physicians' knowledge and care preferences for Parkinson's disease. Movement Disorders. 2007;22(5):704–707. [PubMed]
  • Wallace AE, MacKenzie TA, Weeks WB. Women's primary care providers and breast cancer screening: Who's following the guidelines? American Journal of Obstetrics and Gynecology. 2006;194(3):744–748. [PubMed]
  • Wilson IB, Landon BE, Hirschhorn LR, McInnes K, Ding L, Marsden PV, Cleary PD. Quality of HIV care provided by nurse practitioners, physician assistants, and physicians. Annals of Internal Medicine. 2005;143(10):729–736. [PubMed]
  • World Health Organization. Primary Health Care Now More Than Ever. World Health Organization; 2008.