Does State-Level Nurse Practitioner Scope-of-Practice Policy Affect Access to Care?

There is heated debate surrounding policy reform granting full state-level nurse practitioner (NP) scope of practice (SOP) in all U.S. states. NP SOP policy is argued to impact access to care; however, a synthesis of empirical studies assessing this relationship has yet to be performed. Our study fills this critical gap by systematically reviewing studies that examine this relationship. We apply Aday and Andersen’s Access Framework to operationalize access to care. We also use this framework to map components of access to care that may relate to NP SOP through concepts identified in this review. Our findings suggest that full state-level NP SOP policy is associated with increases in various components of access to care, but additional work is needed to evaluate causality and underlying mechanisms behind this policy’s effect on access. This work is necessary to align research, practice, and policy efforts surrounding NP SOP with healthcare accessibility.

Keywords: advanced practice, nurse practitioner, policy, access, systematic review

More than half of Americans suffer personally, societally, and economically from having inadequate access to health care (Agency for Healthcare Research and Quality [AHRQ], 2015; Health Resources and Services Administration [HRSA], 2017; Ritchie, 2014). Improving access to care is a national priority; objective 1.3 of the U.S. Department of Health and Human Service (DHHS) 2018–2022 Strategic Plan aims to “improve Americans’ access to healthcare and expand choices of care and service options” (DHHS, 2018). Policy reform aimed at removing state-level scope of practice (SOP) restrictions for nurse practitioners (NP) has been debated as a strategy to increase access to care since the establishment of the NP role in 1965 (Keeling, 2015). However, there is heated debate surrounding this strategy, with only half of all U.S. states implementing full NP SOP policy (American Association of Nurse Practitioners [AANP], 2018). Furthermore, limited research has assessed the impact of changing state-level NP SOP on access to care (Xue, Ye, Brewer, & Spetz, 2016). The state-to-state variation and debate surrounding this policy and the lack of research on this topic raise the question of whether full NP SOP improves patient access to care. A greater empirical understanding of if and how NP SOP regulation affects access to care is needed to inform policy efforts to remove, maintain, or amend state-level NP SOP policies.

State-level NP SOP policy is commonly categorized as “full,” “reduced,” or “restricted,” although there are granular differences within each of these categories ( Figure 1 ). In 2017, 24 states with “full” NP SOP, the least restrictive policy, enable NPs to manage all aspects of patient care, including practicing and prescribing, without physician supervision. Sixteen states require physician supervision to provide select practice or prescriptive activities, which is categorized as “reduced” NP SOP policy. Eleven states with “restrictive” NP SOP policies require physician supervision for all practice and prescription activities (AANP, 2018).

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Overview of state-level regulation of NP SOP Policy in 2017.

Note. NP = nurse practitioner; SOP = scope of practice.

There are several reasons that NPs may be able to improve access to care. The current need for increased access to care is related to an increasing aging population, an increase in demand for services as people become increasingly insured in the United States, and a shortage of primary care (PC) providers in select areas (HRSA, 2013; Obama, 2016; Wishner & Burton, 2017). The NP workforce may impact access to care because NPs are a rapidly growing PC provider type, are more likely to provide care for underserved populations than other provider types, and provide high-quality, cost-effective care (Buerhaus, DesRoches, Dittus, & Donelan, 2015; Institute of Medicine, 2011; Martsolf, Auerbach, & Arifkhanova, 2015; Naylor & Kurtzman, 2010; Stanik-Hutt et al., 2013).

Support for removing restrictive NP SOP policies is related to the notion that these policies inhibit strategically using the NP workforce at the fullest capacity to increase access to care (Hain & Fleck, 2014). Restrictive NP SOP policies may inhibit an NP’s ability to deliver all healthcare services that the NP is trained to perform (Institute of Medicine, 2011). Physician supervision requirements within restrictive NP SOP policies may make it difficult for NPs to provide care to people living in low-resource areas, as there are fewer physicians per population available in these areas to possibly supervise NPs (Goodfellow et al., 2016). Physicians may also require NPs to compensate them financially for their supervision, making it more difficult for NP-led practices to remain financially viable or to care for publicly insured or uninsured patients (Hain & Fleck, 2014).

Opposition to less restrictive NP SOP policies stems largely from physician stakeholder groups, arising from concerns that removing NP SOP restrictions may negatively affect patient safety and outcomes (Cassidy, 2012; Donelan, DesRoches, Dittus, & Buerhaus, 2013; Hain & Fleck, 2014; Isaacs & Jellinek, 2013). In fact, one study found political spending by physician groups influenced a state’s likelihood of maintaining restrictive NP SOP policies while spending by hospital groups influenced a state’s likelihood of removing restrictive NP SOP policies (McMichael, 2017). However, studies have failed to demonstrate that NP-delivered care is unsafe or of poor quality. Numerous studies, including randomized controlled trials, have demonstrated that the quality of NP-delivered care is equal to or better than physician-delivered care in similar care settings (Horrocks, Anderson, & Salisbury, 2002; Lenz, Mundinger, Kane, Hopkins, & Lin, 2004; Newhouse et al., 2011; Stanik-Hutt et al., 2013).

Although multiple studies have demonstrated NPs’ ability to provide high-quality care, a greater understanding of the relationship between varying NP SOP policies and access to care is needed to substantiate policy efforts aimed at removing or maintaining restrictive NP SOP policies. To date, the only systematic review that examines the effect of NP SOP policy on various aspects of care, including access, identified a single article as addressing access to care, possibly due to a restrictive definition of access to care (Xue et al., 2016). Aday and Andersen’s (1974) “A Framework for the Study of Access to Medical Care” describes the complexities of the concept “access” to include not only the use of health services, but also interacting factors such as how the characteristics of the healthcare system influence use. Xue et al. (2016) describe utilization and access as separate concepts and do not define access, possibly leading to an incomplete depiction of literature that addressed the effects of NP SOP policy on access. Because a relationship between NP SOP and access is often cited in political debates and research studies surrounding state-level NP SOP, it is paramount that literature reviews on this topic fully depict this relationship. This review broadens Xue et al.’s (2016) definition of access to care according to a well-established access-to-care theoretical framework and finds 13 studies, instead of one, that address this relationship.

Purpose

The purpose of our review was guided by the need for a systematic understanding of what is currently known about the relationship between state-level NP SOP policy and access to care. The results of this review can be used to better align future research and policy efforts with improving care delivery. We applied Aday and Andersen’s “Framework for the Study of Access” to operationalize the various components of access to care. We also used this framework to map components of access to care that may relate to NP SOP policy through concepts and relationships identified from studies in this review.

Conceptual Framework

Aday and Andersen (1974) operationalized the broad construct of access into a framework that incorporates five concepts, developed through examination of relevant access-to-care literature ( Figure 2 ). This framework operationalizes access by delineating how (1) health policy affects processes of care including (2) characteristics of the health delivery system and (3) characteristics of the population at risk. These characteristics, in turn, affect the patient outcomes of (4) utilization of health services and (5) consumer satisfaction with health services. Based on data availability, population-level outcomes are often assessed instead of individual patient-level outcomes (Concepts 4 and 5). Furthermore, the framework describes how characteristics of the health delivery system (Concept 2) can affect characteristics of the population-at-risk (Concept 3) and how the utilization of health services (Concept 4) and consumer satisfaction (concept 5) can affect each other. This framework was used to guide our conceptualization of access to care throughout this review, in which our policy of interest was NP SOP policy, and the results of our review were synthesized with respect to the categories of access defined by Aday and Andersen (1974).

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Aday and Andersen’s (1974) “Framework for the Study of Access to Medical Care.”

Table 1 presents further detail on how the access concepts from this framework were specifically operationalized for use in this study with respect to NP SOP policy. More specifically, NP SOP policy may impact the health workforce and the organization of this workforce and the propensity of providers to care for underserved populations. This, in turn, may impact the level and pattern of consumer utilization of services and consumer satisfaction with these services. It should be noted that although this framework provides a novel way to broadly examine the relationships between NP SOP policy and various components of access to care, it does not wholly explain all of the factors that may contribute to this relationship.

Table 1.

Operationalizing Aday and Andersen’s (1974) Access Concepts for Use in This Review.

Access to Care ConceptOperational Definition: How the Health Policy of State-Level NP SOP Has Implications On:
Characteristics of Health Delivery SystemProcesses of careWorkforce resources and the organization of these resources.
Characteristics of Population-at-Risk Specific populations, especially traditionally underserved populations.
Utilization of Health ServicesPatient- (or population-) level outcomes of careThe level and pattern of patient use of healthcare services.
Consumer Satisfaction Patient reported satisfaction with available health services, including convenience, costs, coordination, courtesy, information, and quality.

Method

A systematic literature review was conducted following the seven steps for research synthesis outlined by Cooper (2016). The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) was followed for analysis and presentation of data from all stages of review (Moher, Liberati, Tetzlaff, & Altman, 2009).

Our research purpose was formulated through a preliminary review of the literature and other reports, and through round-table discussion with researchers with experience studying the healthcare workforce and access to care. A health sciences librarian was consulted to strengthen our search strategy. We searched the electronic databases The Cumulative Index to Nursing & Allied Health Literature (CINAHL), PubMed, PsychInfo, and EconLit for all empirical studies published from database conception—August 2017, using the following keywords search strategy: (“advanced practice registered nurse” or “advanced practice nurs*” or “nurse practitioner” or “aprn” or “apn” or “np”) AND (“scope of practice” or “legislat*” or “regulat*” or “policy”) AND (“access*”). Peer-reviewed quantitative and qualitative studies that reported empirical findings related to NP SOP policy and any of the access concepts, as defined by Aday and Andersen’s framework (1974), and were written in English were included for full review. The references of selected articles were scanned for additional relevant articles. Articles that did not explicitly address the relationship between NP SOP policy and access to care were excluded. Studies conducted outside of the United States were also excluded because the state-level NP SOP policies being assessed are unique to U.S. healthcare regulation. Two authors blindly and independently screened all studies for eligibility at both the title/abstract and full text review stage using Covidence systematic review software (Melbourne, Australia). Disagreements in screening were resolved by consensus. Our search strategy is presented in Figure 3 .

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PRISMA flow diagram.

Note. PRISMA = Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

A standardized data extraction template was used to collect data on the research purpose, theoretical framework, study design, setting, demographics, methods, data collection, results, and quality. The quality of studies was considered based on select criteria from quality appraisal guidelines from the National Institutes of Health, including participant sampling criteria, sample size justification, effect size calculation, study design, and loss to follow-up (National Institutes of Health National Heart, Lung, and Blood Institute [NHLBI], 2014). Studies were not excluded a priori based on quality in this review due to a limited number of studies conducted that addressed our purpose. Two authors independently extracted 15% of articles to reach consensus on types and depth of information extracted. A single author extracted the remainder of articles with secondary approval of information extracted from another author. Disagreements were resolved by consensus. After all data were extracted, results were collectively analyzed, categorized, and presented by common themes and conclusions, guided by access concepts outlined in Aday and Andersen’s (1974) framework.

Results

Study Characteristics

The search yielded 608 studies, of which 38 full-text articles were reviewed, and 13 articles met all inclusion criteria for this review. Study characteristics are described in Table 2 . All studies used retrospective cross-sectional study designs. Three studies assessed repeated cross-sections over time (Kuo, Loresto, Rounds, & Goodwin, 2013; Kurtzman et al., 2017; Stange, 2014). All studies used secondary data, except one that analyzed primary data collected through a survey (Poghosyan et al., 2015). In nine articles, a framework was used to guide the study. However, only three of these studies used a theoretical framework to specifically conceptualize access to care (Cross & Kelly, 2015; Sonenberg, Knepper, & Pulcini, 2015; Sonenberg & Knepper, 2017).

Table 2.

Quality of Studies.

StudyNational SampleJustification for Sample SizeCalculation of Effect SizeData at Multiple Time PointsLack of Significant Missing Data
Barnes et al. (2017)YesYesNoNoYes
Cross and Kelly (2015)YesYesNoNoNo
DesRoches et al. (2013)YesYesNoNoYes
Graves et al. (2016)YesYesNoNoYes
Kuo, Loresto, Rounds, and Goodwin (2013)YesYesNoYesYes
Kurtzman et al. (2017)YesYesNoYesYes
Mobley et al. (2016)NoYesNoNoYes
Poghosyan et al. (2015)NoYesYesNoYes
Oliver, Pennington, Revelle, and Rantz (2014)YesYesNoNoYes
Reagan and Salsberry (2013)YesYesNoNoYes
Sonenberg, Knepper, and Pulcini (2015)YesYesNoNoYes
Sonenberg and Knepper (2017)NoYesNoNoYes
Stange (2014)NoYesNoYesYes

Note. Appraised from NHLBI National Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies. NHLBI = National Institutes of Health National Heart, Lung, and Blood Institute.

Sample and Setting Characteristics

The unit of analysis in studies ranged from insurance beneficiaries, providers, practices, provider-patient visits, and health service areas. Participants from five studies were Medicare and/or Medicaid beneficiaries (Cross & Kelly, 2015; DesRoches et al., 2013; Kuo et al., 2013; Mobley et al., 2016; Reagan & Salsberry, 2013). A national sample was used in nine studies. Ten studies examined access to PC services, while others implied examination of PC services (Oliver, Pennington, Revelle, & Rantz, 2014), examined community health centers (Kurtzman et al., 2017), or examined facilities with mammography services (Mobley et al., 2016).

Quality

Relationship Between NP SOP and Access-to-Care Themes

The results were categorized into four access-to-care themes based on Aday and Andersen’s (1974) framework: (a) characteristics of the health delivery system, (b) characteristics of the population-at-risk, and patient-level outcomes of (c) utilization of health services and (d) consumer satisfaction with health services. Study characteristics and measures of NP SOP policy and access to care are detailed in Table 3 . Study results categorized by access-to-care theme are presented in Table 4 . Because categorization of NP SOP varied throughout studies in this review, we standardized reporting and discussing NP SOP categories as least to most restrictive ( Figure 1 ).

Table 3.

Characteristics of Studies.

Full SOP (least restrictive states) Without full SOP (restrictive to most restrictive states combined) Odds that an individual NP works in PC vs. specialty practice Whether the practice accepts Medicaid Restricted Usual source of care Appointment wait times Difficulties with access and cost

SOP based on various dimensions including physician oversight and prescribing (specific categories NI)

Geographic distribution of NPs Restricted % of population in low-, medium-, and high-accessibility areas Number of geographically accessible PC MDs, NPs, and PAs per 100,000 population Number of uninsured by provider type

Most analyses divided into (a) Independent practice and prescription authority, (b) Independent practice but requiring supervision for prescription, or (c) Requiring physician supervision for practice and prescription

Odds of having an NP as the PC provider Estimated number of NPs per 100,000 state residents Full-practice independence vs. not full-practice independence Full-prescriptive independence vs. not full-prescriptive independence Quality Indicators (smoking, depression, hyperlipidemia management) Service Utilization (physical exam, education and counseling, imaging, medication) Referral Patterns (return visits, referral to MD) Restrictive Mammography use in a 3-year period

MA—NPs can independently treat and diagnose, but physician collaborative agreement required to prescribe

NY—Physician collaborative agreement required for NP treatment, diagnosis, and prescription Restricted Avoidable hospitalizations Readmission rates after inpatient rehabilitation Nursing home resident hospitalizations State overall health outcomes 4 previously collected sets of data No restriction Intermediate restrictions Most restrictive practices Pearson Report 2008 Number of NPs per 100,000 population Change in numbers of NPs between 2001 and 2008 Growth rate in NPs for those HSAs that had a positive number of NPs

State Practice Act language, prescription supervision, PC case management, workers’ compensation, diagnosis and treatment, Modified Sekscensky Index

Number of NPs licensed to practice per 100,000 population Health outcomes: obese, diabetic, heart disease deaths per 100,000, hypertension Least restrictive NP SOP laws: CO, UT Most restrictive NP SOP laws: AL, MS

Select measures include population demographics, health professional shortage areas, number of NPs per 100,000 residents, number of NPs per 100,000 uninsured residents

Practice index based on practice environment for NPs and PAs in 2000 and index ranks of physician oversight, prescriptive authority, and reimbursement policies

2004 HRSA files Usual source of care Number of office-based visits Use of preventative services

Note. AANP = American Association of Nurse Practitioners; APRN = advanced practice registered nurse; ARF = area resource files; CDC = Centers for Disease Control; CNM = certified nurse midwife; FFS = fee-for-service; HRSA = Health Resources and Services Administration; HSA = health service area; MCBS = Medicare Current Beneficiaries Survey; MD = medical doctor; MEPS = Medical Expenditure Panel Survey; NAMCS = National Ambulatory Medicare Care Survey; NI = not included; NP = nurse practitioner; PA = physician assistant; PC = primary care; SK&A = health practitioner database; SOP = scope of practice.

Table 4.

Study Results by Access to Care Theme.

More NPs working in PC vs. specialty care in states that had policies for both full SOP & 100% NP Medicaid reimbursement *

Fewer NPs working in PC vs. specialty care in states without policies for 100% NP Medicaid reimbursement * or policies for both full SOP and 100% NP Medicaid reimbursement **

No difference in number of NPs working in PC vs. specialty care in states with full SOP policy but not 100% Medicaid reimbursement policy

Practices were more likely to accept Medicaid if an NP was present and had either or both full SOP or 100% Medicaid reimbursement policies ***

Usual source of care not affected by SOP Wait times higher in states with full vs. reduced or restricted SOP ** More difficulties accessing care in states with full vs. reduced SOP * Fewer difficulties with cost in full vs. reduced or restricted SOP states *

Higher ratios of NPs’ billing Medicare for fee-for-service beneficiaries in states with least restrictive SOP †

Greater PC NPs per 100,000 population in states with full vs. restrictive SOP * Greater PC NPs per 100,000 population in rural counties in states with full vs. restrictive SOP

States with less restrictive SOP had up to 40% more PC NPs in some areas, but no significant difference in the share of overall population in low-accessibility areas across SOP categories

PC NPs and PAs were the largest shares of the PC workforce in rural areas of states with full SOP and the smallest share in urban areas of states with reduced and restricted SOP

Greatest increase in number of NPs per 100,000 residents was in states with least restrictive SOP requirements *

Patients in states with the least restrictive SOP had greater odds of having an NP as their PC provider *

Independent prescription associated with increased likelihood of NP-visits including health education and medication use * , and MD-visits including health education **

Independent practice associated with increased incidence of MD-visits including depression treatment ** , and likelihood of NP-visits resulting in physician referral **

Patients in states with expanded vs. restrictive SOP had enhanced odds of mammography use in both urban and rural areas *

NPs in Massachusetts (MA) vs. New York (NY) reported better practice environments * More NPs in MA vs. NY worked in community health centers *** More NPs in MA vs. NY worked in rural locations ***

Decreased rates of avoidable hospitalization and readmission within 30 days of discharge for beneficiaries in states with full vs. without full SOP ***

Decreased rates of annual hospitalization for beneficiaries in nursing homes in states with full vs. without full SOP

More NPs per 100,000 population and greater growth rate of NPs in states with least vs. most restrictive SOP ***

More per capital NPs in states with least vs. most restrictive SOP **** No difference in number of NPs between states with intermediate vs. most restrictive SOP

Growth in number of NPs (2001–2008) was >100% no SOP restrictions, 92% in intermediate SOP, and 73% restrictive SOP states †

% of population in poverty not affected by SOP Lower uninsurance rates in states with least vs. most restrictive SOP *** No association between SOP and number of NPs licensed to practice per 100,000 population

Fewer NPs per 100,000 residents and uninsured residents in Colorado (CO) & Utah (UT) vs. Mississippi (MS) †

Greater ratio of funding to number of rural health clinics in CO & UT vs. Alabama (AL) & MS †

Fewer practitioners needed to remove health professional shortage area designations in CO & UT vs. AL & MS †

Lower % of population in rural settings, Higher % of population that is a minority in CO & UT vs. AL & MS † Lower % of adults reporting not seeing a doctor due to costs in CO & UT vs. AL & MS † Greater supply of NPs alone did not affect healthcare utilization

PC utilization was responsive to NP provider supply in areas that grant nonphysician clinicians the least restrictive SOP **

Expansions in NP prescriptive authority were associated with increases in patient-care utilization **

Note. NP SOP results in this table are presented in context of how NP SOP was measured in parent study, but were standardized and discussed as least versus most restrictive in the section “Results” of this review. MD = medical doctor; NP = nurse practitioner; PA = physician assistant; PC = primary care; SOP = scope of practice—refers specifically to state-level NP SOP policy; vs. = versus.

† Statistical significance not assessed.

NP SOP and characteristics of the health delivery system.

Eight studies addressed the relationships between NP SOP policy and the characteristics of the health delivery system by addressing characteristics of the NP workforce (Barnes et al., 2017; DesRoches et al., 2013; Graves et al., 2016; Kuo et al., 2013; Poghosyan et al., 2015; Reagan & Salsberry, 2013; Sonenberg & Knepper, 2017; Sonenberg et al., 2015). NPs were more likely to work in PC, bill Medicare, or practice in states with the least restrictive NP SOP policies (Barnes et al., 2017; DesRoches et al., 2013; Graves et al., 2016; Kuo et al., 2013; Reagan & Salsberry, 2013). Furthermore, there was more growth in the number of NPs in states with the least restrictive SOP policies (Kuo et al., 2013; Reagan & Salsberry, 2013). Last, patients in states with the least restrictive NP SOP policies were more likely to have an NP as their PC provider (Kuo et al., 2013). The results of most studies showed a positive association between less restrictive NP SOP policy and NP workforce capacity. However, Sonenberg et al. (2015) reported no significant association between NP SOP policy and number of NPs licensed to practice per 100,000 population. And Sonenberg and Knepper (2017) reported more NPs per 100,000 residents in a state with more restrictive NP SOP policies compared with two states with less restrictive NP SOP policies.

Other studies examined relationships between state-level NP SOP policy and the characteristics of the NP workforce including the relative balance of specialty and PC provided by NPs and variations in NP-reported practice environments by state NP SOP policy. One study examined the impact of NP SOP policy on the NP workforce for PC versus specialty care. This study reported that NPs were more likely to work in PC versus specialty care in states with both full SOP and 100% Medicaid reimbursement policies; however, this difference did not hold in states with full SOP but without 100% Medicaid reimbursement policies (Barnes et al., 2017). Finally, when comparing two states with differing NP SOP policies, NPs in the state with the less restrictive NP SOP policy reported better practice environments (Poghosyan et al., 2015).

NP SOP and characteristics of the population-at-risk.

Five studies addressed the relationships between NP SOP policy and the characteristics of the population-at-risk, including the underserved populations of Medicaid beneficiaries and patients living in rural and high-poverty locations (Barnes et al., 2017; Graves et al., 2016; Poghosyan et al., 2015; Reagan & Salsberry, 2013; Sonenberg & Knepper, 2017). Some studies report that in states with the least restrictive NP SOP policies, NPs were more likely to work in PC, provide care in rural and high-poverty areas, and accept Medicaid (Barnes et al., 2017; Graves et al., 2016). Another study reports that a state with a less restrictive NP SOP policy has more NPs working in community health centers and in rural locations (Poghosyan et al., 2015) than a comparison state with a more restrictive NP SOP policy. Another study reported there was a lower percent of the population that was

NP SOP and utilization of health services.

Four studies addressed the relationships between NP SOP policy and the patient- or population-level outcomes of utilization of health services. Utilization was assessed by proportion of patients receiving a referral to another provider, receiving health education services, receiving preventive services, and avoiding hospitalizations and 30-day readmissions (Kurtzman et al., 2017; Mobley et al., 2016; Oliver et al., 2014; Stange, 2014). There was greater use of preventive services and decreased rates of avoidable hospitalizations, hospital readmissions within 30 days discharge from rehabilitation, and hospitalizations of nursing home patients in states with the least restrictive NP SOP policies (Mobley et al., 2016; Oliver et al., 2014; Stange, 2014). One study reported that only some components of full NP SOP policy were associated with increased likelihood of a patient visit to an NP including health education services and prescription of a medication. This study also reported an increased likelihood of patients receiving a referral to a physician from an NP at Community Health Centers in states with SOP policies that allow NPs to practice without physician supervision (Kurtzman et al., 2017). Finally, Stange (2014) reported that a larger supply of NPs, without considering other state- and patient-level factors, did not significantly affect healthcare utilization.

NP SOP and patient satisfaction with care.

Two studies in this review assessed patient satisfaction with care as indicated by patient reported usual source of care, wait times, difficulties accessing care, and difficulties with cost of care (Cross & Kelly, 2015; Sonenberg & Knepper, 2017). While one study reported a smaller percentage of the population not seeking care due to costs in two states with less restrictive versus two other states’ most restrictive NP SOP policies (Sonenberg & Knepper, 2017), contradictory findings from another study reported increased patient difficulties with cost in states with the least restrictive NP SOP policies (Cross & Kelly, 2015). This study also found that patient satisfaction with usual source of care and wait times was worse in states with the least restrictive NP SOP policies (Cross & Kelly, 2015).

Results Conceptualized by Aday and Andersen’s (1974) Framework

We used Aday and Andersen’s (1974) framework as a novel approach to map components of access to care that may relate to NP SOP policy through concepts and relationships identified in this review. The components of access to care related to NP SOP policy were determined through the results of this review. Possible relationships between these components of access were considered through the original relationships between concepts in Aday and Andersen’s (1974) framework. The relationships between the components of access to care were conceptual and not necessarily tested by the studies in this review. Figure 4 applies the review findings to Aday and Andersen’s (1974) framework to map components of access to care related to NP SOP policy. By considering what components of access to care relate to NP SOP policy and the relationships between these components, future work can begin assessing the underlying mechanism for how state-level NP SOP policy affects access to care.

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Results of review conceptualized by Aday and Andersen’s (1974) “Framework for the Study of Access to Medical Care.”

All components of Aday and Andersen’s (1974) framework are addressed by the studies in this literature review, suggesting that this body of research is capturing the multifaceted definition of access. Further analyzing the results jointly through the framework demonstrated that although there are 13 studies assessing the impact of NP SOP policy on access to care, these studies individually addressed different concepts of access. Although eight studies assessed the impact of NP SOP policy on characteristics of the health delivery system, the impact of NP SOP policy on patient satisfaction with care was largely understudied. Future work should place emphasis on assessing the more understudied aspects of access to care.

Last, the relationships between components of access to care outlined in Aday and Andersen’s (1974) framework offer an opportunity to consider relationships between multiple components of access to care in future studies. For example, future work may consider the “characteristics of population at risk” as a moderator between the impacts of health policy on patient utilization of health services. Because NPs may be more likely to care for traditionally underserved populations, the impact of increasing the NP workforce may have a greater effect on access to care for these populations than for others.

Discussion

Although stakeholders agree that there is a need to improve U.S. access to high-quality care, a greater understanding of how and if policies aimed at improving access actually achieve their goal is needed. This need is heightened when a policy is subject to professional debate surrounding its effectiveness, as is policy change surrounding NP SOP. This review is the first to assess the relationship between state-level NP SOP policy and access to care and to use Aday and Andersen’s (1974) framework to broadly conceptualize and apply a multifaceted definition of access. This review adds to the understanding of how NP SOP policy is associated with access to care and can be used to guide further research and policy efforts surrounding state-level NP SOP policy.

The relationship between NP SOP policy and the characteristics of the health delivery system, primarily the NP workforce, was the aspect of access to care most studied in this review. Most studies that assessed the impact of NP SOP policy on the NP workforce found that less restrictive NP SOP policy was associated with a greater number of NPs or growth of NPs (Barnes et al., 2017; DesRoches et al., 2013; Graves et al., 2016; Kuo et al., 2013; Reagan & Salsberry, 2013). This may perhaps be due to NPs’ reporting better practice environments in states with less restrictive NP SOP policies (Poghosyan et al., 2015). Studies that did not support this association acknowledged that their study design was limited by using a state-level unit of analysis (Sonenberg et al., 2015) or that their study was not generalizable because they compared four select states (Sonenberg & Knepper, 2017). Collectively, studies assessing the impact of NP SOP policy on the NP workforce provide evidence that less restrictive NP SOP is positively associated with characteristics of the health delivery system related to the NP workforce.

A recent review on factors that affect the NP workforce’s potential in reducing health disparities supports that restrictive state-level NP SOP policy may limit an NP’s contribution to reducing health disparities (Poghosyan & Carthon, 2017). Unfortunately, there were few studies that addressed whether NP SOP policy is related to the characteristics of the population-at-risk, and some studies had conflicting results. The difference in results may be attributed to greater statistical power to detect differences in studies with more micro- versus macro-level unit of analyses due to differences in sample size and standard deviations (Li & Dai, 2013). For example, Reagan and Salsberry (2013) examined health service areas as their unit of study, while Barnes et al. (2017) and Graves et al. (2016) examined practice sites and providers, respectively.

One study reported fewer socioeconomic and health disparities in two states with less versus two states with more restrictive NP SOP policies (Sonenberg & Knepper, 2017). Although it is possible that the socioeconomic and health differences in states with and without full NP SOP policy are related to the policy itself, it is also possible that states with fewer disparities were more likely to allow full NP SOP policy. If the former is correct, it builds a case for less restrictive NP SOP policies to reduce socioeconomic and health disparities. If the latter is correct, future work should assess why states that had better socioeconomic and health outcomes were the ones choosing to have full NP SOP in their state. Ultimately, there is insufficient evidence from this review on the impact of NP SOP policy on care for underserved populations, highlighting a need for additional studies that examine this relationship.

Utilization of primary care services was greater (Kurtzman et al., 2017; Mobley et al., 2016; Stange, 2014), and utilization of acute health services was lower in states with less restrictive NP SOP policies (Oliver et al., 2014), providing some evidence of a relationship between less restrictive NP SOP policies and utilization of health services. These findings are consistent with evidence that suggests that increased market competition is associated with higher quality over time (Rivers & Glover, 2008). The relationship between increased competition and improved quality could explain why Kurtzman et al. (2017) found that some aspects of physician-delivered care in Community Health Centers, such as depression treatment, were better in states with less restrictive NP SOP policies. Furthermore, these findings may be a result of decreased administrative burden on physicians in states with less restrictive NP SOP policy, increasing time available for patient care (Traczynski & Udalova, 2018).

A critique of removing NP physician supervision requirements is that it may result in increased utilization of patient referrals to medical doctors (MD) by NPs (Isaacs & Jellinek, 2013). Kurtzman et al. (2017) found that patient-visits to NPs in states with less restrictive NP SOP were more likely to result in referrals to physicians; they suggest this may be due to NPs in full NP SOP states having fewer resources and, therefore, relying more heavily on referral networks; NP uncertainty when physician supervision is unavailable; or NP fear of liability or malpractice. It is also possible that the increase in referrals to MDs is a necessary secondary outcome of NPs’ caring for more complex patients in states with full NP SOP policies. Ultimately, the rationale for why there may be increased referrals to MDs, and whether this reflects inefficacies versus necessities in care delivery, remains unclear and merits further investigation.

Although other studies report high patient satisfaction with care delivered by NPs (Stanik-Hutt et al., 2013), there was insufficient evidence available from this review on the relationship between NP SOP policy and patient satisfaction with convenience, coordination, and cost of care. Patient satisfaction with care was the least studied aspect of access to care found in this review, and the two studies that addressed this relationship were considered lower quality because they contained significant amounts of missing data and only assessed two states, respectively (Cross & Kelly, 2015; Sonenberg & Knepper, 2017). The results of these studies also contradicted one another. For these reasons, additional evidence is needed to make conclusions on if NP SOP is related to patient satisfaction with care.

Although the results of this study generally support that less restrictive NP SOP is positively associated with select aspects of access to care, additional evidence is required. We were unable to make conclusions of effect of NP SOP policy on access to care because most studies in this review evaluated associative, not causal relationships. The results of this review highlight multiple avenues for future research. A greater use of longitudinal and natural experimental designs, understanding of the mechanism by which NP SOP policy affects access, and use of access theories to broadly study NP SOP’s effect on multiple aspects of access will enhance conclusions about the relationship between NP SOP and access.

Future research should consider which policies, both within NP SOP and additional to NP SOP policy, that have the greatest effect on improving access to care can help guide policy efforts. For example, one study in this review suggested that the relationship between NP SOP and access is amplified when other healthcare policies are taken into account, such as 100% Medicaid reimbursement for NPs (Barnes et al., 2017). Furthermore, evaluating which parts of NP practice regulated by SOP policy have the greatest impact on access to care is needed to better guide future policy efforts. Studies in this review suggested that changes to full SOP, not from restrictive to reduced, may be required to actualize significant improvements in patient access to care (Barnes et al., 2017; Kuo et al., 2013; Reagan & Salsberry, 2013). Last, although this review focused on state-level NP SOP policy, intersection of this state-level policy with organizational policy should be considered. For example, organizational policies may circumvent state-level policies and allow the NPs to perform greater or reduced roles than the state-level NP SOP policy specifies. In addition, organizations that support models of care that optimize the use of NP-delivered care, such as nurse-managed health clinics, may increasingly be considered to impact access (Westat, 2015). Ultimately, the intersection of organization- versus state-level NP SOP policy poses an interesting avenue for further research.

Finally, most previous studies do not use access-to-care theories to consider the multifaceted components of access to care in relation to NP SOP. In the future, researchers should clearly articulate which aspect of access to care their study focuses on to help other researchers and policy makers make consistent comparisons and conclusions across studies. Analysis of the results from our review through Aday and Andersen’s (1974) framework highlights a need for future research that not only addresses understudied components of access, but begins to evaluate how, rather than if, state-level NP SOP policy is related to access to care. This review maps several components of access to care that may be associated with NP SOP, and uses an access-to-care framework to consider how these components are interrelated, to aid in these future efforts.

This review is limited by lack of inclusion of the so-called “grey” literature and lack of assessment of patient health outcomes. Although we found relevant white papers, dissertations, or reports from organizations such as Westat and The RAND Corporation that contained informative data on the relationship between NP SOP and access, we did not include these sources because they were not published in a peer-reviewed journal (Martsolf & Kandrack, 2016; Westat, 2015). Furthermore, studies assessing the impact of NP SOP on access have been published since this systematic review was conducted (Traczynski & Udalova, 2018; Xue et al., 2018). Although these sources were not included to uphold the methodological robustness of a systematic review, they should be considered in addition to the results of this review to inform policy decisions surrounding NP SOP. This review also did not assess patient health outcomes. As this review was based on access to care as defined by Aday and Andersen’s (1974) framework, we did not purposefully search for or report patient health outcomes related to NP SOP. However, we acknowledge that the goal of improved access to care is to ultimately improve patient outcomes, which should be considered in future studies. These limitations should be acknowledged when using the results of this review to guide future research and policy on NP SOP.

In conclusion, the results of the review provide preliminary evidence that NP SOP policy is associated with select aspects of access to care, but warrant further investigation of these relationships. Additional evidence is required to assess the relationship between NP SOP policy and the characteristics of the population-at-risk and consumer satisfaction with care. This positive association between NP SOP and the characteristics of the health delivery system related to the NP workforce and consumer utilization of health services suggest that NP SOP can be further assessed as a policy lever to improve access to care. Ultimately, however, further research is required before policy efforts to remove or maintain NP SOP regulation based on its effect on access to care can be substantiated.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was partially supported by a National Service Research Award Pre-Doctoral Traineeship from the Agency for Health Care Research and Quality sponsored by the Cecil G. Sheps Center for Health Services Research, University of North Carolina at Chapel Hill, Grant No. 5T32 HS000032, and by The Alex and Rita Hillman Foundation through the Hillman Scholars Program in Nursing Innovation at the University of North Carolina at Chapel Hill.