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Mundinger MO, Kane RL, Lenz ER, Totten AM, Tsai W, Cleary PD, Friedewald WT, Siu AL, Shelanski ML. Primary Care Outcomes in Patients Treated by Nurse Practitioners or PhysiciansA Randomized Trial. JAMA. 2000;283(1):59–68. doi:10.1001/jama.283.1.59
Context Studies have suggested that the quality of primary care delivered by
nurse practitioners is equal to that of physicians. However, these studies
did not measure nurse practitioner practices that had the same degree of independence
as the comparison physician practices, nor did previous studies provide direct
comparison of outcomes for patients with nurse practitioner or physician providers.
Objective To compare outcomes for patients randomly assigned to nurse practitioners
or physicians for primary care follow-up and ongoing care after an emergency
department or urgent care visit.
Design Randomized trial conducted between August 1995 and October 1997, with
patient interviews at 6 months after initial appointment and health services
utilization data recorded at 6 months and 1 year after initial appointment.
Setting Four community-based primary care clinics (17 physicians) and 1 primary
care clinic (7 nurse practitioners) at an urban academic medical center.
Patients Of 3397 adults originally screened, 1316 patients (mean age, 45.9 years;
76.8% female; 90.3% Hispanic) who had no regular source of care and kept their
initial primary care appointment were enrolled and randomized with either
a nurse practitioner (n = 806) or physician (n = 510).
Main Outcome Measures Patient satisfaction after initial appointment (based on 15-item questionnaire);
health status (Medical Outcomes Study Short-Form 36), satisfaction, and physiologic
test results 6 months later; and service utilization (obtained from computer
records) for 1 year after initial appointment, compared by type of provider.
Results No significant differences were found in patients' health status (nurse
practitioners vs physicians) at 6 months (P = .92).
Physiologic test results for patients with diabetes (P
= .82) or asthma (P = .77) were not different. For
patients with hypertension, the diastolic value was statistically significantly
lower for nurse practitioner patients (82 vs 85 mm Hg; P = .04). No significant differences were found in health services
utilization after either 6 months or 1 year. There were no differences in
satisfaction ratings following the initial appointment (P = .88 for overall satisfaction). Satisfaction ratings at 6 months
differed for 1 of 4 dimensions measured (provider attributes), with physicians
rated higher (4.2 vs 4.1 on a scale where 5 = excellent; P = .05).
Conclusions In an ambulatory care situation in which patients were randomly assigned
to either nurse practitioners or physicians, and where nurse practitioners
had the same authority, responsibilities, productivity and administrative
requirements, and patient population as primary care physicians, patients'
outcomes were comparable.
The many pressures on the US health care system and greater focus on
health promotion and prevention have prompted debates about primary care workforce
needs and the roles of various types of health care professionals. As nurse
practitioners seek to define their niche in this environment, questions are
often raised about their effectiveness and appropriate scope of practice.
Several studies conducted during the last 2 decades1-4
suggest the quality of primary care delivered by nurse practitioners is equal
to that of physicians. However, these earlier studies did not directly compare
nurse practitioners and physicians in primary care practices that were similar
both in terms of responsibilities and patient panels.
Over time, payment policies and state nurse practice acts that constrained
the roles of nurse practitioners have changed. In more than half the states,
nurse practitioners now practice without any requirement for physician supervision
or collaboration, and in all states nurse practitioners have some level of
independent authority to prescribe drugs.5
Additionally, nurse practitioners are now eligible for direct Medicaid reimbursement
in every state, direct reimbursement for Medicare Part B services as part
of the 1997 Balanced Budget Act,6 and commercial
insurance reimbursement for primary care services within limits of state law.
Finally, state law determines whether nurse practitioners are eligible for
hospital admitting privileges, either by regulating access at the state level
or by allowing local hospital boards to decide. The combination of authority
to prescribe drugs, direct reimbursement from most payers, and hospital admitting
privileges creates a situation in which nurse practitioners and primary care
physicians can have equivalent responsibilities. The present study is a large
randomized trial designed to compare patient outcomes for nurse practitioners
and physicians functioning equally as primary care providers.
The opportunity to compare the 2 types of providers was made possible
by several practice and policy innovations at the Columbia Presbyterian Center
of New York Presbyterian Hospital in New York City. In 1993 when the medical
center sought to establish new primary care satellite clinics in the community,
the nurse practitioner faculty were asked to staff 1 site independently for
adult primary care. This exclusively nurse practitioner practice was to be
similar to the clinics staffed by physicians. All are located in the same
neighborhood, serve primarily families from the Dominican Republic who are
eligible for Medicaid, and follow the policies and procedures of the medical
center. The nurse practitioner practice, the Center for Advanced Practice,
opened in the fall of 1994.
New York State law allows nurse practitioners to practice with a collaboration
agreement that requires the physician to respond when the nurse practitioner
seeks consultation. Collaboration does not require the collaborating physician
to be on site and requires only quarterly meetings to review cases selected
by the nurse practitioner and the physician. The state also grants nurse practitioners
full authority to prescribe medications, as well as reimbursement by Medicaid
at the same rate as physicians. The medical board granted nurse practitioners
who were faculty members in the school of nursing hospital admitting privileges,
thereby making the basic outpatient services, payment, and provider responsibilities
the same in the nurse practitioner and physician primary care practices. Additionally,
nurse practitioners and physicians in the study were subject to the same hospital
policy on productivity and coverage, and a similar number of patients were
scheduled per session in each clinic.
While it has been posited that nurse practitioners have a differentiated
practice pattern focused on prevention with lengthier visits,7
this study was purposely designed to compare nurse practitioners and physicians
as primary care providers within a conventional medical care framework in
the same medical center, where all other elements of care were identical.
Nurse practitioners provided all ambulatory primary care, including 24-hour
call, and made independent decisions for referrals to specialists and hospitalizations.
The Spanish language ability of the nurse practitioners and physicians was
similar, although the physicians had somewhat better Spanish facility on average.
All of the nurse practitioners (n = 7) and most of the physicians (n = 11)
had limited knowledge of Spanish, and 6 physicians were either fluent or bilingual.
Staff who served as interpreters were available at each study site. The central
hypothesis was that the selected outcomes would not differ between the patients
of nurse practitioners and physicians.
Between August 1995 and October 1997, adult patients were recruited
consecutively at 1 urgent care center and 2 emergency departments that are
part of the medical center. Patients who reported a previous diagnosis of
asthma, diabetes, and/or hypertension, regardless of the reason for the urgent
visit, were oversampled to create a cohort of patients for whom primary care
would have an impact on patient outcomes, as has been postulated in previous
studies.8,9 Patients were screened
by bilingual patient recruiters and asked to participate if they had no current
primary care provider at the time of recruitment and planned to be in the
area for the next 6 months. The study was approved by the institutional review
board of Columbia Presbyterian Medical Center. After an oral explanation of
the consent form, written informed consent was obtained from each patient
(both English and Spanish explanations and forms were available).
Those who provided informed consent were randomly and blindly assigned
to either the nurse practitioner or 1 of the physician practices. Different
assignment ratios were used during the recruitment period. Initially the ratio
was 2:1, with more patients assigned to the nurse practitioner practice, because
it opened after the physician practices and was able to accept more new patients.
Subsequently, the ratio was changed to 1:1 as the nurse practitioner practice's
patient panel increased. Despite this change, the mean number of days between
the urgent visit at which patients were recruited and the follow-up appointments
was similar (8.6 days for patients assigned to nurse practitioners compared
with 8.9 days for patients assigned to physicians).
Recruited patients were then offered the next available appointments
at the assigned clinic, and project staff made reminder calls the day before
the appointments. Patients who missed their appointment were offered another
appointment at the assigned practice. After patients kept their initial appointments,
they were considered enrolled in the study and eligible for follow-up data
Patients were told which provider group they were assigned to after
randomization, and the type of provider could not be masked during the course
of care. Patients who refused to participate or were deemed ineligible for
the study were given follow-up primary care appointments by the study recruiters
to the same practices. Additionally, during the study period, all practices
received new patients from usual sources such as hospital discharges, recommendations
from friends and family, referrals from other physicians, direct access by
the patients themselves, and advertising. The study did not require a different
process of care or documentation for enrolled patients.
At the initial visit, the patients became a part of the nurse practitioner
or physician practices' regular patient panel, and all subsequent appointments,
care, and treatments were arranged through the practice site of the assigned
primary care nurse practitioner or physician. The primary care nurse practitioners
and physicians had the same authority to prescribe, consult, refer, and admit
patients. Furthermore, they used the same pool of specialists, inpatient units,
and emergency departments. No attempt was made to differentiate study patients
from other patients in the practice or to influence the practice patterns
of the participating nurse practitioners and physicians. However, patients
were free to change their source of medical care during the study. Medicaid
in New York is currently fee-for-service and patients could go to other providers,
go to a specialist directly, or use the emergency department without notifying
their primary care provider. Approximately 3% of patients (n = 43) went to
another clinic after keeping the first randomly assigned appointment, and
9% (n = 116) went to multiple primary care clinics during the 6-month period.
At the time of recruitment, patients provided demographic and contact
information and completed the Medical Outcomes Study 36-Item Short-Form Health
Survey (SF-36). After the initial primary care visit, interviewers contacted
the enrolled patients either by telephone or in person, if necessary, to administer
a satisfaction questionnaire. Six months after this initial appointment, the
enrolled patients were again contacted and asked to complete a second, longer
interview. The decision to interview patients 6 months after the initial primary
care visit was based on prior survey experience with this patient population.10 The primary care patients served by the medical center
are primarily immigrants and frequently change residences, travel between
New York and their countries of origin, and have interruptions in telephone
service. Attempts were made to locate all enrolled patients for this follow-up,
including those who could not be located for the initial satisfaction interview.
At the 6-month interview, the SF-36 and the satisfaction questionnaire were
repeated, and additional questions were asked about health services utilization.
A research nurse accompanied the interviewers, and for patients who reported
a diagnosis of asthma, diabetes, or hypertension, physiologic data were collected.
Data on all health services utilization at the assigned practice and
all other medical center sites were obtained from the medical center computer
records for both the 6 months prior to recruitment and for 6 months and 1
year after the initial primary care appointment. These data were collected
for all patients who were enrolled, including those who could not be located
for the 6-month follow-up interview. Utilization data were also available
for patients who were recruited but who did not keep their initial primary
care appointment and therefore were not enrolled in the study. For these patients,
the data were collected for the 6 months prior to recruitment and 6 months
and 1 year after the date of the missed appointment they were given at recruitment.
The SF-36 was used as a baseline and follow-up measure of health status.
This instrument elicits patient responses to 36 questions designed to measure
8 health concepts (general health, physical function, role-physical, role-emotional,
social function, bodily pain, vitality, and mental health)11
or to create 2 summary scores (physical component summary and mental component
summary).12 The origin and logic of the item
selection, as well as the psychometrics and tests of clinical validity, have
been reported by the survey's developers.13,14
Additionally, the survey's utility for monitoring general and specific populations,
measuring treatment benefits, and comparing the burden of different diseases
has been documented in 371 studies published between 1988 and 1996.15,16 For example, the SF-36 has been used
to measure differences in function between chronically ill patients with and
without comorbid anxiety disorder17; has demonstrated
that it can detect changes in health status that correspond to clinical profiles
for 4 common conditions18; and has shown that
it reflects changes in health status that correspond to a predicted clinical
course for elective surgery patients.19
Patient satisfaction was measured by using "provider-specific" items
from a 15-item satisfaction questionnaire used in the Medical Outcomes Study.20 Three items related to clinic management were included
in the survey to provide the medical center administration with information
about patients' perceptions of the clinic, but those items were not intended
for use in the comparison of providers.
The survey instruments used in the study were written in English and
then translated into Spanish. The bilingual members of the study team reviewed
the Spanish versions to ensure that the meaning had not been changed. Approximately
80% (78.8% at recruitment and 83.7% at 6 months) of the interviews were conducted
Physiologic measures included disease-specific clinical measurements
taken by a research nurse at the time of the 6-month follow-up interview.
Blood pressure was determined for patients with hypertension, peak flow for
those with asthma, and glycosylated hemoglobin for those with diabetes.
Utilization data included hospitalizations, emergency department visits,
urgent care center visits, visits to specialists, and primary care visits
within the Columbia Presbyterian Medical Center system. Only visits with a
nurse practitioner or physician at a primary care site were counted as primary
care. Specialty visits were defined as visits to a medical specialty clinic
or specialist physician office. Emergency department and urgent care center
visits were combined before analysis.
Recruitment and enrollment goals were established based on estimates
of the sample size needed to detect a difference of 5 points on a 100-point
scale for the SF-36 scores on all scales when comparing 2 groups with repeated
measures. As the randomization ratio was projected to change during the course
of the study with availability of appointments, it was projected that the
final ratio between the 2 groups would be 1 patient in the physician group
for every 1.5 patients in the nurse practitioner group. The sample size estimates
for unequal groups were extrapolated from those presented by the instrument's
developer for equal groups, assuming α = .05, 2-tailed t test, and power of 80%. Differences of more than 5 points are considered
clinically and socially relevant, according to the guidelines for the interpretation
of the survey.11
Baseline demographics and health status for the nurse practitioner and
physician groups at randomization and following enrollment were compared using χ2 and t tests. Ten of the 12 satisfaction questions
were factor analyzed (the 11th question that asks whether the patient would
recommend the clinic to family and friends was left as a separate item; an
item about medication instructions was dropped, as it was not applicable to
the majority of respondents who were not prescribed any medications at their
first visit). There were 3 factors with eigenvalues greater than 1, indicating
that they represented reasonable constructs. The first, "provider attributes"(Cronbach α
= .80) rated the provider on technical skills, personal manner, and time spent
with the patient on a 5-point scale from poor to excellent. "Overall satisfaction"
(Cronbach α = .86) was the factor created from 2 items addressing the
quality of care received and overall satisfaction with the visit. The "communications"
factor (Cronbach α = .59) combined 5 areas in which patients may have
had problems understanding the provider's assessment and advice. Mean scores
were computed for each factor.
Using the data collected at recruitment, mean baseline scores on the
SF-36 for the scales and summary scores were used to establish the comparability
of the nurse practitioner and physician groups in terms of health status.
Four types of analyses were conducted using the SF-36 as an outcome measure.
The first 2 included t tests to compare mean scores
for nurse practitioner and physician patients at 6-month follow-up (both unadjusted
and adjusted for baseline demographics and health status) and baseline to
6-month change scores. The third was a subgroup analysis designed to compare
the sickest patients. Patients whose baseline score on the physical component
summary of the SF-36 was in the bottom quartile (sickest) of the study sample
were selected, and 6-month follow-up SF-36 scores were compared using the
same analyses used for the total sample.
The fourth analysis classified patients into categories according to
the change from baseline to follow-up in each patient's individual scores
on the summary measures. This analysis was modeled on a comparison of patients
treated in health maintenance organization and fee-for-service systems.21 The SE of measurement was used to create 3 categories:
"same" (change not greater than what would be expected by chance), "better"
(improved more than expected), and "worse" (declined more than expected).12 While these definitions are based on a statistical
construct, they provide results that may be more clinically relevant than
mean scores or mean change in scores over time. A χ2 test was
then used to compare the distribution of the nurse practitioner and physician
patients among these groups. In addition, the change from baseline to follow-up
for the entire sample was compared using paired t
Ranges and mean values for the physiologic measures were obtained, and
mean values for the 2 groups were compared using t
For the analyses of health services utilization, data were obtained
for 6 months prior to the date of recruitment, 6 months after, and 1 year
after the first primary care visit. Neither the recruitment visit nor the
assigned primary care visit was included. Comparisons between the nurse practitioner
and physician patients' health services utilization after enrollment were
made using χ2 tests (unadjusted) and Poisson regression (adjusted).
To compare the utilization prior to recruitment with that following, signed
rank tests were used.
The 159 patients (12.1%) who, after the first visit, either went to
a clinic other than the one assigned or to multiple primary care clinics were
maintained in the initially assigned group for the analyses, consistent with
an intent-to-treat analysis. All analyses were repeated without these 159
patients, and the results were the same.
Of the 3397 patients screened and given follow-up appointments, 41.6%
were not randomized because they either refused to participate (11.2%) or
did not meet the screening criteria (30.4%). Of the 1981 patients who were
randomized, 1181 (59.6%) were assigned to the nurse practitioner clinic and
800 (40.4%) to the physician clinics. The average age of the randomized patients
was 44.4 years and 74.6% were female; 84.9% were Hispanic, 8.8% were black,
and 1.1% were white. There were no statistically significant differences in
the demographics or health status of the patients randomized to nurse practitioners
or physicians (Table 1).
The 1316 patients (66.4%) who kept their initial primary care appointments
following randomization were considered enrolled in the study. This rate is
comparable to the normal rate of appointments (65%) kept at the participating
clinics (P. Craig, MA, RN, e-mail message, August 4, 1999). Compared with
the 665 patients (32.4%) who did not keep their appointments, those who did
(the enrolled patients) differed significantly at baseline in several respects.
Enrolled patients were older (45.9 vs 41.3 years); a higher proportion were
female (76.8% vs 70.2%) and Hispanic (90.3% vs 82.9%); a higher percentage
reported a history of 1 or more of the selected chronic conditions (53.7%
vs 45.0%); and they had to wait fewer days for their follow-up appointments
(7.8 vs 10.7). These findings are consistent with other studies of patient
behavior relative to keeping or missing appointments.22-24
Our analysis of the data available on patients who did not keep their
primary care appointments found no differences in health services utilization
after 1 year among the patients assigned to the nurse practitioner group and
The difference in the retention rates between recruitment and enrollment
for the nurse practitioner group (68.2%) and the physician group (63.8%) was
statistically significant (χ21 = 4.3, P = .04). However, neither the patients who enrolled nor those who
failed to keep their appointments differed significantly between the nurse
practitioner and physician groups in terms of baseline demographics, SF-36
scores, or patient-reported prior diagnosis of the selected chronic conditions
Among the nurse practitioner patients, 59% saw the same provider for
all primary care visits in the first year after the initial visits compared
with 54% of the physician patients, and this difference was not statistically
significant (χ21 = 2.7, P
Initial satisfaction interviews were completed for 90.3% (n = 1188)
of all patients who made a first clinic visit (90.8% of the nurse practitioner
group and 89.4% of the physician group). Almost 92% of all completed interviews
took place within 6 weeks of the initial appointment.
Six-month interviews were completed for 79% of all enrolled patients
(80.5% of the nurse practitioner group and 76.7% the physician group). This
completion rate is considered high for a transient immigrant population and
is comparable to or better than that achieved by other studies in the area
served by the medical center. The majority of completed interviews (91.4%)
took place between 180 and 240 days after the initial appointment. The most
common reasons for loss to follow-up were the inability to locate the patient
(65.9%) or that the patient had moved out of the area (17%). A small number
of patients (23 [2.8%] in the nurse practitioner group and 16 [3.1%] in the
physician group) refused to complete the interview when they were contacted.
Five patients (2.9%) were located but were unable to complete the interview
due to physical limitations or mental illness, and 3 patients (1.1%) were
deceased. Figure 1 summarizes the
participation rates at each major stage in the study.
There were no significant differences in the scores between nurse practitioners
and physicians for any of the satisfaction factors after the first visit (Table 2). At the 6-month interview there
were no statistically significant differences in "overall satisfaction" or
"communications" factors or in willingness to refer the clinic to others.
The difference in mean score for the "provider attributes" factor, however,
was significant, with the physician group rating providers higher than the
nurse practitioner group (4.22 vs 4.12 out of a possible 5; P = .05). The provider attribute consists of patients' ratings of the
providers' technical skill, personal manner, and time spent with the patient.
The clinical significance of a 0.1 difference on a 5.0 scale is unlikely.
Overall, the health status of the study group improved from baseline
to follow-up, and the improvement was statistically significant on every scale
There were no significant differences between the nurse practitioner
and physician patients on any scale or summary score at 6 months. This is
true for both the unadjusted scores and scores adjusted for demographics and
baseline health status. The additional analysis (not shown) of the summary
scores, using the change categories of "same," "better," and "worse" to characterize
the clinical course of each patient, also revealed no significant differences
between provider types.
Finally, 152 nurse practitioner patients and 103 physician patients
were defined as the sickest (health status scores in the bottom quartile of
the sample at baseline) and their scores analyzed separately. Again, there
were no differences between nurse practitioner and physician patients in scale
scores or summary measures at 6 months (both unadjusted and adjusted), nor
did the change in scores from baseline to follow-up differ between nurse practitioner
and physician patient groups.
The physiologic measures taken at the time of the interview for patients
who reported 1 of the selected chronic illnesses were not statistically significantly
different between the nurse practitioner and physician patients for asthma
and hypertension. The mean peak flow measurements for the 64 physician patients
with asthma was 292 L/min, compared with 297 L/min for the 107 nurse practitioner
patients (t test = −0.29, P = .77). Glycosylated hemoglobin mean value for the 46 physician patients
with diabetes was 9.4% vs 9.5% for the 58 nurse practitioner patients (t test = −0.22, P = .82).
For patients with hypertension, there was no statistically significant
difference in the systolic reading: 139 mm Hg for the 145 physician patients
and 137 mm Hg for the 211 nurse practitioner patients (t test = 1.08, P = .28). The mean diastolic
reading, however, was statistically significantly lower for the nurse practitioner
patients at 82 mm Hg compared with 85 mm Hg for the physician patients (t test = 2.09, P = .04).
For our comparison of outcomes we analyzed utilization of health care
services for nurse practitioner and physician patients who enrolled in the
study by keeping their initial primary care appointment. There were no statistically
significant differences between the nurse practitioner and physician patients
for any category of service during either the first 6 months or the first
year after the initial primary care visit for either unadjusted or adjusted
use rates (Table 4). When the
utilization analyses were repeated for the subsets of "sickest" patients as
defined in the "Self-reported Health Status" section above, no differences
were found in the health care services utilization between the nurse practitioner
and physician patients (Table 5).
In the 6 months and 1 year after the initial primary care visit, enrolled
patients in both groups made significantly more primary care and specialty
visits and fewer emergency/urgent visits than in the 6 months prior to recruitment.
The percentage of enrolled patients hospitalized was not significantly different
for either 6 months or 1 year after the initial primary care appointment.
This study was designed to compare the effectiveness of nurse practitioners
with physicians where both were serving as primary care providers in the same
environment with the same authority. The hypothesis predicting similar patient
outcomes was strongly supported by the findings of no significant differences
in self-reported health status, 2 of the 3 disease-specific physiologic measures,
all but 1 of the patient satisfaction factors after 6 months of primary care,
and in health services utilization at 6 months and 1 year.
The difference between the nurse practitioner and physician patients'
mean ratings of satisfaction with provider attributes was small but statistically
significant. It may be attributable to the fact that the nurse practitioner
practice was moved to a new site after 2 years and before recruitment and
data collection were completed; the physician practices were not moved during
the study period. When the "provider attribute" subscale scores for the nurse
practitioner and physician patients whose 6-month follow-up period overlapped
this move were compared, the ratings by nurse practitioner patients were significantly
lower than those of the corresponding physician patients (4.16 vs 4.36; P = .04). There was no significant difference in ratings
among patients not affected by the move. Additional research will be needed
to determine whether this is a persistent difference or if it results from
conditions unique to this study.
A statistically significant, but small, difference was discerned in
the mean diastolic blood pressure of patients with hypertension, with the
nurse practitioner group having a slightly lower average reading at 6 months.
Given the size of this change and the lack of differences in self-reported
health status, there does not seem to be an obvious reason for this difference.
Although insufficient statistical power to discern differences has been
a problem in much of the previous research comparing nurse practitioners and
physicians, the sample size in this study was adequate to test the hypothesized
similarity of nurse practitioner and physician groups. At the end of the study,
power calculations were repeated using final sample size and the means and
SDs from these data. These revealed that the sample size was adequate to detect
differences from baseline to follow-up between the 2 patient groups of less
than 5 points for 6 of the 8 scales (3.2 for general health; 3.3 for vitality;
3.4 for mental health; 3.4 for social function; and 4.2 for bodily pain) and
less than 6 points on 2 scales (5.9 on role-physical and role-emotional).
This magnitude of difference is similar to differences commonly reported in
studies comparing groups21,25
and in studies of change over time within 1 group.17,26
There is evidence that the outcome measures chosen were sensitive enough
to discern any important differences. The SF-36 is a widely used outcome measure
and its sensitivity has been documented in several studies.11,18,27
In this study, there were sizable and statistically significant changes for
both nurse practitioner and physician patients in all scale scores and summary
measures from baseline to follow-up. Some improvement would be expected, even
over a 6-month period with or without primary care, following the urgent care
visits at which subject recruitment occurred; the SF-36 did detect improvement.
The utilization indicators are in widespread use in cross-sectional and longitudinal
studies. With the exception of number of hospitalizations, which stayed the
same in both groups, these measures also changed significantly over time.
Strengths of this study included adequate sample size and the ability
to randomize patients to equivalent clinical settings and to providers with
equal responsibilities. However, there were also several limitations.
Patients could not be randomized at the point of initial contact with
the provider. Because the nurse practitioner and physician practice sites
were geographically separate, patients had to be randomized when they were
recruited in the emergency department or urgent care center to give them follow-up
appointments at various locations with different appointment schedules. This
time and location gap likely contributed to the loss of almost one third of
the sample between randomization and enrollment. Although this is substantial,
it is within the range reported in similar randomized trials.28
While the loss rate was significantly different for the nurse practitioner
and physician groups, there is no reason to suspect that this represents a
systematic violation of the protocol or any compromise of randomization. Patients
dropped out before receiving care, and the dropout rate was higher for those
assigned to the traditional model of physician care. This suggests that assignment
to the new model of nurse practitioner care did not negatively influence patient
behavior. There is no evidence of selection bias in that there were no significant
differences in demographics, baseline health status, or prerecruitment health
services utilization patterns between nurse practitioner and physician randomized
patients, for either those who enrolled or those who did not keep their appointments.
A 1-year follow-up for SF-36 and patient satisfaction would have been
more useful than taking these measures at 6 months. In part, we believed a
population with limited access to health care would show changes in these
measures in 6 months. But more influential in the decision regarding follow-up
was the knowledge that this population is difficult to track because of changing
addresses, changing eligibility for Medicaid, and frequent extended trips
out of the country. Although we do have service utilization data for both
6 months and 1 year, data on satisfaction and self-perceived health status
were not collected for 1 year.
Finally, the study had some characteristics that limit the generalizability
of results. It was conducted in medical center–affiliated, community-based
primary care clinics, which may differ from individual providers or small
group practices. The providers were faculty from a university medical center,
hence were not necessarily typical of those in nonacademic practice settings.
The patients were predominantly immigrants from the Dominican Republic who
were eligible for Medicaid and many did not speak English. This differs from
the setting in which many commercially insured patients receive primary care
but does resemble other academic, public and safety net providers, and the
Medicaid populations they serve. While the setting and patient population
are limitations, they are also what permitted randomized assignment and an
environment in which nurse practitioners and physicians were able to function
equally as primary care providers. The ability to do this type of study, even
in a setting atypical for some patients, adds significant weight to the results
from prior studies that have demonstrated the competence of nurse practitioners.
Who provides primary care is an important policy question. As nurse
practitioners gain in authority nationally with commercially insured and Medicare
populations now accessing nurse practitioner care, additional research should
include these populations. As cost and quality issues pervade the public debate
on managed care, those who are the first-line health care providers become
pivotal resources in the emerging health care system. Nurse practitioners
have been evaluated as primary care providers for more than 25 years, but
until now no evaluations studied nurse practitioners and physicians in comparable
practices using a large-scale, randomized design. The results of this study
strongly support the hypothesis that, using the traditional medical model
of primary care, patient outcomes for nurse practitioner and physician delivery
of primary care do not differ.