FREE NEJM E-TOC    HOME   |   SUBSCRIBE   |   CURRENT ISSUE   |   PAST ISSUES   |   COLLECTIONS   |   Search Term  Advanced Search

Sign in | Get NEJM's E-Mail Table of Contents — Free | Subscribe

Previous Volume 331:1266-1271 November 10, 1994 Number 19 Next

Abstract Add to Personal Archive Add to Citation Manager Notify a Friend E-mail When Cited PubMed Citation

ABSTRACT

Background Most proposals to increase access to primary care in the United States emphasize increasing the proportion of generalist physicians. Another approach is to increase the number of physician assistants, nurse practitioners, and certified nurse-midwives.

Methods We analyzed variations in the regulation of nurse practitioners, physician assistants, and certified nurse-midwives in all 50 states and the District of Columbia. Using a 100-point scoring system, we assigned numerical values to specific characteristics of the practice environment in each state for each group of practitioners, awarding a maximum of 20 points for legal status, 40 points for reimbursement for services, and 40 points for the authority to write prescriptions. We calculated coefficients for the correlation of summary measures of these values within states with estimates of the supply of practitioners per 100,000 population.

Results There was wide variation among states in both practice-environment scores and practitioner-to-population ratios for all three groups of practitioners. We found positive correlations within states between the supply of physician assistants, nurse practitioners, and certified nurse-midwives and the practice-environment score for the state (Spearman rank-correlation coefficients, 0.63 [P<0.001], 0.41 [P = 0.003], and 0.51 [P<0.001], respectively). Positive associations were also found in the states between the supply of generalist physicians and the supply of physician assistants (r = 0.54, P<0.001) and nurse practitioners (r = 0.35, P = 0.014). Nevertheless, in the 17 states with the greatest shortages of primary care physicians, favorable practice-environment scores were still associated with higher practitioner-to-population ratios for physician assistants (r = 0.68, P = 0.003), nurse practitioners (r = 0.54, P = 0.026), and certified nurse-midwives (r = 0.42, P = 0.09).

Conclusions State regulation of physician assistants, nurse practitioners, and certified nurse-midwives varies widely. Favorable practice environments are strongly associated with a larger supply of these practitioners.

Although the education, licensure, and regulation of nurse practitioners and physician assistants differ, many have similar job descriptions¹⁶. They diagnose illness, perform physical examinations, order and interpret laboratory tests, establish and carry out treatment plans, suture wounds, and provide preventive health services. Each profession is about 25 years old in the United States. Physician assistants are salaried employees who by law must work under the supervision of a physician. Of the 22,300 physician assistants practicing in 1992, 44 percent worked in primary care specialties, and another 8 percent were in emergency medicine. The majority were educated in two-year training programs. About 34 percent of physician assistants worked in rural areas¹⁷.

In some states, nurse practitioners can establish independent practices and be reimbursed directly for their services. Because the states have no common definition of nurse practitioners, estimates of their number vary widely. Through 1992, about 42,600 employed registered nurses had received formal training as nurse practitioners beyond their professional education as nurses¹⁸; estimates of the number practicing as nurse practitioners ranged from 21,900¹⁹ to 27,200²⁰. The majority were educated in certificate programs averaging about one year in length; 4 of every 10 had master's degrees. About three quarters were in primary care. Eighteen percent of nurse practitioners worked outside metropolitan areas in 1992¹⁹.

Certified nurse-midwives are registered nurses with advanced education in the provision of prenatal, perinatal, postpartum, newborn, and routine gynecologic care. About 61 percent had master's degrees in 1991²¹. Since 1971, national certification as a nurse-midwife has required graduation from an accredited program for nurse-midwifery and the passing of an examination administered by the American College of Nurse-Midwives. In 1992, 43 states recognized certified nurse-midwives in their statutes or regulations²². About half of all states allowed direct reimbursement for the services of a certified nurse-midwife. In 1992, between 3500 and 4300 certified nurse-midwives were eligible to practice in private offices, community health centers, free-standing birthing centers, and other health care settings²³ (and unpublished data). Certified nurse-midwives attended 4.1 percent of all deliveries in the United States in 1991²⁴. Between 11 and 22 percent practiced in rural areas^13,24.

Methods

Practice environments in the states were assessed by reviewing journal articles and legislation and by consulting with researchers, legal scholars, and professional organizations. In all jurisdictions, information was sought about conditions in 1992. Specific criteria are shown in Table 1.

View this table: [in this window] [in a new window]   Table 1. Scoring System Used to Quantify the Practice Environment in States in Regard to Physician Assistants, Nurse Practitioners, and Certified Nurse-Midwives.

 
A 100-point scoring system was constructed for each group; a maximum of 20 points was allocated if practitioners had legal status as professionals, 40 points if reimbursement for their services was required, and 40 points if they had the authority to write prescriptions. More weight was given to the second and third categories because the simple recognition of professional identity entailed in the conferring of legal status alone was considered less important; however, when equal weight was given to each of the three major categories, the results did not change substantially. Points were allocated within each category and then totaled. A score of 100 represented the most favorable environment, and a score of 0 the least favorable. The assessment was performed consistently for all the states in a given discipline, but the actual criteria for the disciplines varied because of professional and regulatory differences. Thus, comparison of scores between states is more appropriate within a discipline than between disciplines.

The practice environments for physician assistants were quantified primarily on the basis of information from the American Academy of Physician Assistants²⁵ and other published studies^8,26. The practice environments for nurse practitioners were quantified on the basis of information from published studies^15,27. The practice environments for certified nurse-midwives were quantified on the basis of information from the American College of Nurse-Midwives^23,28 and a survey by the Office of the Inspector General of the Department of Health and Human Services²¹. Supplemental information on all three groups of practitioners was obtained from the 1993 annual report of the Physician Payment Review Commission⁴.

Estimates of the supply of nonphysician practitioners in each state were obtained from various sources (Table 2). The estimates of 27,200 practicing nurse practitioners and 4300 certified nurse-midwives were the only available estimates that provided state-specific figures. The estimates of the number of physician assistants do not include federal employees. The supply of generalist physicians was estimated as the total number of nonfederal allopathic physicians actively involved in patient care who designated themselves as being in general practice, family practice, general internal medicine, or general pediatrics in the 1992 Area Resource File²⁹. Practice-environment scores and estimates of the supply of practitioners were calculated independently. Data from the Bureau of the Census on state populations in 1992 were obtained from the American Medical Association³⁰. Estimates of the percentage of each state's population that was living in areas designated as having a shortage of primary care were obtained from the Bureau of Primary Health Care of the Department of Health and Human Services³¹.

View this table: [in this window] [in a new window]   Table 2. Practitioner-to-Population Ratios and Practice-Environment Scores for Physician Assistants, Nurse Practitioners, and Certified Nurse-Midwives According to State, 1992.

 
Because the practice-environment scores we developed had non-normal distributions, they were analyzed with nonparametric methods. States were ranked according to their practice-environment scores and the number of practitioners per 100,000 population (practitioner-to-population ratios). Rank-correlation coefficients were derived for pairs of individual practitioner-to-population ratios and practice-environment scores, according to the method of Spearman³².

We calculated partial correlation coefficients that compared the supply of nonphysician practitioners with that of generalist physicians, with control for the state population³³. All P values are based on two-tailed tests.

Results

There was wide variation in both state practice-environment scores and practitioner-to-population ratios for all the groups of practitioners (Table 2, Figure 1). For physician assistants, the practice-environment scores ranged from a high of 100 in the state of Washington to 0 in Mississippi. Twenty states had scores of 90 or higher; 14 had scores below 50. Practitioner-to-population ratios varied from a high of 24.6 physician assistants per 100,000 population in Maine to a low of 0.2 in Mississippi. Twenty-one states had 10 or more physician assistants for every 100,000 people, whereas 13 states had 5 or fewer.

View larger version (11K): [in this window] [in a new window]   Figure 1. Correlation of the Practitioner-to-Population Ratio with the Practice-Environment Score for Three Groups of Practitioners in Each of the 50 States and the District of Columbia, 1992. The numbers of practicing, nonfederally employed physician assistants (Panel A), nurse practitioners (Panel B), and licensed, certified nurse-midwives (Panel C) per 100,000 population are shown, with Spearman rank-correlation coefficients and P values for the correlations.

 
Practice-environment scores for nurse practitioners ranged from 100 in Oregon to 14 in Ohio and Illinois. Twelve states scored 86 or above; 19 had scores below 50. The ratios of the number of nurse practitioners to members of the population also varied widely, from 37.2 per 100,000 in the District of Columbia to 2.7 per 100,000 in Nebraska. Twenty-six states had ratios of more than 10, including 10 above 20. In contrast, five states had ratios of 5 or fewer.

Practice-environment scores for certified nurse-midwives ranged from 100 in Minnesota to 25 in Indiana. Six states had scores of 90 or higher; 13 had scores of 50 or less. The number of certified nurse-midwives per 100,000 population was low in all the states, ranging from a high of 6.4 in Alaska to a low of 0.1 in Nebraska. Six states had practitioner-to-population ratios of 4 or above, and 14 had fewer than 1 certified nurse-midwife per 100,000 population.

With a few exceptions, states that had favorable practice-environment scores for one group of practitioners also had favorable scores for the other two groups. States with more favorable practice-environment scores were clustered in the West and Northwest; several states with less favorable scores were in the Southeast.

Among states with generally unfavorable practice environments, the lack of authority to write prescriptions was an important contributor to low scores for all groups. For example, 16 of the 17 states with the lowest practice-environment scores for physician assistants prohibited these practitioners from writing prescriptions, as did 11 of the 17 states with the lowest scores for certified nurse-midwives and 9 of the 17 with the lowest scores for nurse practitioners.

Reimbursement was an important factor in the practice-environment scores for nurse practitioners, but it was somewhat less important for physician assistants, who, as salaried employees, are not reimbursed directly for their services, and for certified nurse-midwives. Of the 17 states with the least favorable practice environments for nurse practitioners, 4 had a score of 0 on the reimbursement scale, and none scored higher than 20 out of a possible 40 points.

Correlations among Groups of Practitioners

We found significant positive correlations for all three groups of practitioners between favorable state practice-environment scores and higher practitioner-to-population ratios (Table 3). Positive associations were also found in the states between the supply of physician assistants and the practice-environment score of nurse practitioners and between the supply of nurse practitioners and the practice-environment score of physician assistants (Table 3). This suggests that in most instances a greater supply of practitioners in one group was not associated with barriers to practice for the other. We examined the possibility that the supply of physician assistants, nurse practitioners, and certified nurse-midwives in a particular state depends on educational opportunities for these practitioners. We analyzed the supply of each group of practitioners in relation to the number of accredited schools in the states in 1992. The results were inconclusive (data not shown). Although several states with schools had a higher-than-average supply of practitioners of the discipline in question, no overall correlation was found between the state-specific supply of practitioners and the number of accredited schools for any group.

View this table: [in this window] [in a new window]   Table 3. Rank-Correlation Coefficients and P Values for Practitioner-to-Population Ratios and Practice-Environment Scores for All States and for the 17 States with the Largest Proportions of People Living in Areas with a Shortage of Primary Care Physicians.

 
To examine the potential effect of competition between physicians and either physician assistants or nurse practitioners, we compared the supply of each group of practitioners with that of generalist physicians in the state. (Certified nurse-midwives were excluded from this analysis because of their relatively small numbers; federally employed physicians were also excluded.) We found significant positive relations between the supply of each group of practitioners and the supply of allopathic generalist physicians (with residents in graduate medical training excluded) after controlling for state population (Table 4). In most states, a greater number of physician assistants and nurse practitioners did not appear to be associated with a lesser supply of generalist physicians.

View this table: [in this window] [in a new window]   Table 4. Partial Correlation Coefficients and P Values for the Comparison of Estimates of the Supply of Physician Assistants and Nurse Practitioners with That of Generalist Physicians and Residents in the 50 States and the District of Columbia, with Control for State Population, 1992.

 
We found a positive correlation in the states between the supply of physician assistants and the number of resident physicians in graduate medical training, suggesting that a disproportionate number of physician assistants may be employed in teaching hospitals (Table 4). No comparable relation was apparent between the supply of nurse practitioners and the number of resident physicians in the states.

Some studies suggest that competition between physicians and nonphysicians has triggered the creation of barriers to practice for nonphysician practitioners in some states^15,34. We therefore compared the supply of generalist physicians in the states with the practice-environment scores for nurse practitioners and physician assistants. No associations were found between the practice-environment scores for either group of practitioners and the supply of generalist physicians, whether resident physicians were included or excluded from the analysis.

Areas with Shortages of Primary Care Physicians

An adequate supply of physician assistants, nurse practitioners, and certified nurse-midwives may be particularly important in areas lacking sufficient numbers of primary care physicians. We repeated some of our analyses for the 17 states with the highest proportions of people living in areas designated as having a shortage of primary care in 1992 (Table 3). These proportions ranged from 11.6 percent of people in North Carolina to 25.0 percent in North Dakota. Three quarters of these areas with primary care shortages were rural. Nonphysician practitioners are not counted in the formula used by the federal government to characterize these areas³¹.

In the 17 states, favorable practice-environment scores for physician assistants and nurse practitioners were associated with practitioner-to-population ratios significantly above the national average (Table 3). For certified nurse-midwives there was a similar trend (P = 0.09). The nine states with practice-environment scores of 90 or higher for physician assistants had an average ratio of 13.4 physician assistants per 100,000 people, as compared with 1.8 in the states with scores of 40 or less. The four states with practice-environment scores of 90 or higher for nurse practitioners had an average of 17.5 nurse practitioners per 100,000 people, as compared with 6.4 in the five states with scores of 40 or less. For certified nurse-midwives, the ratios were 1.2 per 100,000 for the two states with scores of 90 or higher, and 0.8 per 100,000 for the four states with scores of 40 or less.

Discussion

Favorable state practice environments for physician assistants, nurse practitioners, and certified nurse-midwives were strongly associated with a greater supply of these practitioners. States with less favorable practice environments had fewer such practitioners for every 100,000 people. In general, practice environments within a state were consistently favorable or unfavorable for all three groups. Inability or limited ability to write prescriptions was a major factor in lowering practice-environment scores for all three groups. Reimbursement issues were important in lowering the scores for nurse practitioners, but they were of lesser importance for physician assistants and certified nurse-midwives.

Our findings do not support the hypothesis that a larger supply of generalist physicians in a state is associated with a less favorable practice environment for nonphysician practitioners. Indeed, we found that the supplies of generalist physicians, physician assistants, and nurse practitioners within states were positively associated. However, states with documented shortages of primary care physicians that had environments favorable to physician assistants and nurse practitioners had more such practitioners than the national average.

Factors other than those we identified affect the practice environment for nonphysicians at the state level. For example, acceptance as professionals by physicians (including the extension of hospital admitting privileges and professional collaboration), inclusion in the terms of private and corporate health insurance policies, ability to obtain malpractice insurance, and acceptance by the public are probably important determinants of the supply of practitioners at the community, regional, and state levels. In addition, because our analysis applied to only one short period, we could not determine whether the greater supply of nonphysician practitioners preceded the removal of barriers to practice, or the reverse.

Our study demonstrates that regulation by the states of physician assistants, nurse practitioners, and certified nurse-midwives varies widely. These findings may help state legislators and regulators reduce specific barriers to practice and thus make these practitioners more available to patients.

Source Information

From the Bureau of Health Professions, Health Resources and Services Administration, Department of Health and Human Services, Rockville, Md. The views expressed in this article are strictly those of the authors. No official endorsement by the Department of Health and Human Services or any of its components is intended or should be inferred.

Address reprint requests to Mr. Sekscenski at the Bureau of Health Professions, Health Resources and Services Administration, Rm. 8-47, 5600 Parklawn Dr., Rockville, MD 20857.

References

1. Budetti PP. Achieving a uniform federal primary care policy: opportunities presented by national health reform. JAMA 1993;269:498-501. [CrossRef][Medline]
2. Kindig DA, Cultice JM, Mullan F. The elusive generalist physician: can we reach a 50% goal? JAMA 1993;270:1069-1073. [Abstract]
3. Rivo ML, Satcher D. Improving access to health care through physician workforce reform: directions for the 21st century. JAMA 1993;270:1074-1078. [CrossRef][Medline]
4. Annual report to Congress 1993. Washington, D.C.: Physician Payment Review Commission, 1993.
5. Starfield B. Primary care: concept, evaluation, and policy. New York: Oxford University Press, 1992.
6. Josiah Macy, Jr., Foundation. Report of the Josiah Macy, Jr., Foundation: for July 1, 1991 through June 30, 1992. New York: The Foundation, 1992.
7. Mundinger MO. Advanced-practice nursing -- good medicine for physicians? N Engl J Med 1994;330:211-214. [Free Full Text]
8. The National Health Service Corps White Paper: proposed strategies for fulfilling primary care professional needs: part II: nurse practitioners, physician assistants, and certified nurse-midwives. Rockville, Md.: National Health Service Corps, 1991.
9. Primary care workforce 2000: federal health policy strategies submitted to Hillary Rodham Clinton and the President's Task Force on National Health Reform. Washington, D.C.: Pew Health Professions Commission, 1993.
10. Brown SA, Grimes DE. Nurse practitioners and certified nurse-midwives: a meta-analysis of studies on nurse primary care roles. Washington, D.C.: American Nurses, 1993.
11. Schaft GE, Cawley J. The physician assistants in a changing health care environment. Rockville, Md.: Aspen Publications, 1987.
12. Clawson DK, Osterweis M, eds. The roles of physician assistants and nurse practitioners in primary care. Washington, D.C.: Association of Academic Health Centers, 1993.
13. Scupholme A, DeJoseph J, Strobino DM, Paine LL. Nurse-midwifery care to vulnerable populations: phase 1: demographic characteristics of the National CNM Sample. J Nurse Midwifery 1992;37:341-348. [Medline]
14. Nichols LM. Estimating costs of underusing advanced practice nurses. Nurs Econ 1992;10:343-351. [Medline]
15. Safriet BJ. Health care dollars and regulatory sense: the role of advanced practice nursing. Yale J Reg 1992;9:417-87.
16. Fowkes V. Meeting the needs of the underserved: the roles of physician assistants and nurse practitioners. In: Clawson DK, Osterweis M, eds. The roles of physician assistants and nurse practitioners in primary care. Washington, D.C.: Association of Academic Health Centers, 1993:69-84.
17. General census data on physician assistants. Alexandria, Va.: American Academy of Physician Assistants, 1993.
18. Bureau of Health Professions. 1992 Sample survey of registered nurses. Rockville, Md.: Department of Health and Human Services, 1993.
19. Bureau of Health Professions. Survey of certified nurse practitioners and clinical nurse specialists: December 1992. Rockville, Md.: Department of Health and Human Services, 1994.
20. Morgan WA. Using State Board of Nursing data to estimate the number of nurse practitioners in the United States. Nurse Pract 1993;18:65-74.
21. Office of the Inspector General. A survey of certified nurse-midwives. Washington, D.C.: Department of Health and Human Services, 1992.
22. Barickman C, Bidgood-Wilson M, Ackerly S. Nurse-midwifery today: a legislative update. J Nurse Midwifery 1992;37:207-207. 
23. National Commission on Nurse-Midwifery Education. Education of nurse-midwives: a strategy for achieving affordable, high-quality maternity care. Washington, D.C.: American College of Nurse-Midwives, 1993.
24. National Center for Health Statistics. Advance report of final natality statistics, 1991. Mon Vital Stat Rep 1993;42:Suppl:1-48. 
25. Gara N. Physician assistant state laws and regulations. 6th ed. Alexandria, Va.: American Academy of Physician Assistants, 1993.
26. Willis J. Barriers to physician assistant practice in primary care and rural medically underserved settings. J Am Acad Physician Assist 1993;6:418-22.
27. Pearson LJ. 1992-93 update: how each state stands on legislative issues affecting advanced nursing practice. Nurse Pract 1993;18:23-38. 
28. Nurse-midwifery today: a handbook of state legislation. Washington, D.C.: American College of Nurse-Midwives, Political and Economic Affairs Committee, 1992.
29. Bureau of Health Professions. Area resource file. Rockville, Md.: Department of Health and Human Services, September 1993.
30. Roback G, Randolph L, Seidman B. Physician characteristics and distribution in the U.S.: 1993 edition. Chicago: American Medical Association, 1993.
31. Bureau of Primary Health Care. Health professions shortage areas. Washington, D.C.: Department of Health and Human Services, 1993.
32. Gibbons JD. Nonparametric methods for quantitative analysis. New York: Holt, Rinehart & Winston, 1976.
33. Kleinbaum DG, Kupper LL. Applied regression analysis and other multivariable methods. North Scituate, Mass.: Duxbury Press, 1978.
34. Ginzberg E, Ostow M. Physician supply strategy: the case of the South. Health Aff (Millwood) 1992;11:193-197. [Medline]

Abstract Add to Personal Archive Add to Citation Manager Notify a Friend E-mail When Cited PubMed Citation

This article has been cited by other articles:

• Sullivan-Marx, E. M. (2008). Lessons Learned From Advanced Practice Nursing Payment. Policy Politics Nursing Practice 9: 121-126 [Abstract]  
• Druss, B. G., Marcus, S. C., Olfson, M., Tanielian, T., Pincus, H. A. (2003). Trends in Care by Nonphysician Clinicians in the United States. NEJM 348: 130-137 [Abstract] [Full Text]  
• Phillips, R. L. Jr., Harper, D. C., Wakefield, M., Green, L. A., Fryer, G. E. Jr. (2002). Can Nurse Practitioners And Physicians Beat Parochialism Into Plowshares?. Health Aff (Millwood) 21: 133-142 [Abstract] [Full Text]  
• Cooper, R. A., Getzen, T. E., McKee, H. J., Laud, P. (2002). Economic And Demographic Trends Signal An Impending Physician Shortage. Health Aff (Millwood) 21: 140-154 [Abstract] [Full Text]  
• Chumbler, N. R., Geller, J. M., Weier, A. W. (2000). The Effects of Clinical Decision Making on Nurse Practitioners' Clinical Productivity. Eval Health Prof 23: 284-304 [Abstract]  
• Ogata, T., Kosho, T., Wakui, K., Fukushima, Y., Yoshimoto, M., Miharu, N. (2000). Short Stature Homeobox-Containing Gene Duplication on the der(X) Chromosome in a Female with 45,X/46,X, der(X), Gonadal Dysgenesis, and Tall Stature. J. Clin. Endocrinol. Metab. 85: 2927-2930 [Abstract] [Full Text]  
• Kosho, T. (1999). Skeletal Features and Growth Patterns in 14 Patients with Haploinsufficiency of SHOX: Implications for the Development of Turner Syndrome. J. Clin. Endocrinol. Metab. 84: 4613-4621 [Abstract] [Full Text]  
• The Medical Education Committee Group for Advancem, (1999). Health Care Reform and Postgraduate Psychiatric Education: Challenges and Solutions. Acad. Psychiatry 23: 1-8 [Abstract] [Full Text]  
• Cooper, R. A., Laud, P., Dietrich, C. L. (1998). Current and Projected Workforce of Nonphysician Clinicians. JAMA 280: 788-794 [Abstract] [Full Text]  
• Cooper, R. A., Henderson, T., Dietrich, C. L. (1998). Roles of Nonphysician Clinicians as Autonomous Providers of Patient Care. JAMA 280: 795-802 [Abstract] [Full Text]  
• Committee on Pediatric Workforce, (1998). Pediatric Workforce Statement. Pediatrics 102: 418-427 [Abstract] [Full Text]  
• Higgins, P. (1996). The nursing profession - a changing role in a changing world. The Journal of the Royal Society for the Promotion of Health 116: 51-56