State-Granted Practice Authority: Do Nurse Practitioners Vote with Their Feet?
Nurse practitioners have become an increasingly important part of the US medical workforce as they have gained greater practice authority through state-level regulatory changes. This study investigates one labor market impact of this large change in nurse practitioner regulation. Using data from the National Sample Survey of Registered Nurses and a dataset of state-level nurse practitioner prescribing authority, a multivariate estimation is performed analysing the impact of greater practice authority on the probability of a nurse practitioner moving from a state. The empirical results indicate that nurse practitioners in states that grant expanded practice are less likely to move from the state than nurse practitioners in states that have not granted expanded practice authority. The estimated effect is robust and is statistically and economically meaningful. This finding is in concert with and strengthens the wider literature which finds states that grant expanded practice authority to nurse practitioners tend to have larger nurse practitioner populations.
Nurse practitioners (s) are, according to the International Council of Nurses, “a registered nurse who has acquired the expert knowledge base, complex decision-making skills, and clinical competencies for expanded practice, the characteristics of which are shaped by the context and/or country in which s/he is credentialed to practice” . In the United States, s are typically masters-prepared registered nurses and have become an increasingly important part of the health care system. They have over time obtained greater practice authority through state-level regulatory changes which has fundamentally altered what an can do as a caregiver. This has, in turn, altered their role in the health care system. In particular, these changes have allowed s to take a more central, independent role in providing health care. While s were initially seen as “physician extenders” by the wider health care industry in the United States, they have become, in many respects, “physician replacers.” Today, in most U.S. states, s can see, diagnose, prescribe, and in general provide care for patients as a general practice physician would. As such, these regulatory changes in practice authority, and the “rise” of the they have ushered in, have fundamentally changed the labor market.
As would be expected in an industry as important as health care, the “rise of the ” has been accompanied by a large body of research. In general, this research can be grouped into four broad categories: their rise as caregivers, the cost and quality of care, populations, and labor market outcomes.
The first body of research details the ’s rise as a primary caregiver. This body, of work traces the origins of the NP in the U.S., their history, and the current role of s in the health U.S. care industry [2–6].
The second and the largest and most active line in the literature investigates the quality and cost of care s provide. A primary finding that can be drawn from this literature is that care provided by s is nearly outcome-indistinguishable to that of physicians [7–12]. In addition, the research shows that care provided by s tends to receive at least as high patient satisfaction ratings as that of physicians [13–15]. This branch of the literature also gives compelling evidence that beyond providing quality care, NP care is also cost effective [16, 17].
A third branch of the literature, and one that is directly pertinent to this research, examines how regulatory changes to practice authority have impacted total NP populations in states. Sekscenski et al.  found, using an index measure of state-level practice authority granted to s, states which granted greater practice authority tended to have larger populations of s than those that did not. The United States Department of Health and Human Services , expanding on Sekscenski et al., also found that the level of practice authority granted was correlated with increased populations. Kalist and Spurr , using a regression framework, found that states that had granted NPs greater practice authority had larger enrolments in masters nursing programs, all else equal.
The fourth and smallest branch of the literature on s examines the impact of regulatory changes in practice authority on their own labor market outcomes. Dueker et al.  made an early contribution to this literature and found the unintuitive result that greater practice authority leads s to have lower incomes. Perry , using a richer data set in which s can be specifically identified, a shortcoming of Dueker et al. work, finds that s who are granted greater practice authority experience significant increases in their incomes relative to NPs who are not granted greater practice authority.
The current project sits at the nexus of the third and fourth bodies of literature. No research that the author is aware has taken a broad, microlevel approach and examined individual location responses to state-level regulation. This research does just that by examining the impact of state-granted practice authority on individual migration choices.
Using a national sample of s spanning 1991 to 2003, a period of significant state-level change in NP regulation, this paper finds that s do “vote with their feet.” In specific, an in a state that has granted greater practice authority to s is less likely to move from the state than otherwise. This result is in concert with—and helps explain—the larger macrolevel literature that practice authority expansions are associated with greater populations in a state as well as the research on the economic impact to s of authority expansions.
There are many reasons an could choose to move from one state to another. Since the work an is allowed to perform is governed by the authority a state grants, it is reasonable to expect the level of practice granted by a state would impact any move decision, even if at the margin. If practice authority is important, one would expect to see s “vote with their feet,” all else equal. If practice authority is not substantially important, moves would not be responsive and move rates would be largely unaffected by changes in state-level practice authority. In either case, the question is an empirical one and policy is directly informed.
A straightforward empirical model that estimates the impact of expanded practice authority on a ’s likelihood to move while controlling for other confounding factors is as follows: where move is a dichotomous variable that equals “1” if the th moves from state in year and “0” otherwise. is a measure of practice authority in a state, equal to “1” if the authority is present in state in year and “0” otherwise. is a matrix of personal characteristics of the th in state in year . is a vector of year dummies to control for year-specific differences and is a vector of state fixed effects.
Equation (1) is estimated both as an Ordinary Least Squares linear probability model and a probit model where the dependent variable is set to zero if the did not move and one if the moved from one state to another.
The data used in the analysis comes from two sources. The first is the National Sample Survey of Registered Nurses (NSSRN). The NSSRN is a probability sample of the universe of Registered Nurses (RN) in the United States and is conducted every four years by the U.S. Department of Health and Human Services. While the focus of the survey is the RN population, s are included and identifiable in the data. The NSSRN observation level is the individual and contains a variety of demographic, geographic, and professional variables. The NSSRN sample years included in this research are 2004, 2000, 1996, and 1992 which corresponds nicely to a large wave of change in state-granted practice authority.
Critical to this study, the NSSRN has information on the state the lived in during the year of the survey as well as where the lived the previous year. While the combined NSSRN data is a repeated cross-section, the questions about where the lived in the year of the survey and where the lived the year prior provides the opportunity to “see” where an individual lived in two contiguous years. This yields a unique opportunity to “see” an individual move or, just as important, not move. A total of 4,103 s are included in the sample aged from 26 to 64. Table 1 provides summary statistics for the sample.
With data on location and demographics of individual s, some measure of state-level practice authority is needed. This study follows the larger literature on s and uses the level of prescriptive authority granted as a general measure of practice authority a state grants. Specifically, whether or not a state grants s some level of controlled substance prescriptive authority is used.
While controlled substance prescriptive authority is an admittedly imperfect measure of authority, it is a widely used component of practice authority in the literature [18, 19, 21]. It also, in a single measure, provides an intuitive and tractable measure of the authority an enjoys in a state.
A by year, by state database of state regulation on controlled substance authority for s was compiled by the author through a review of the annual “Legislative Update” of the journal Nurse Practitioner by Pearson [22–25] and supplemented with research of individual state statues. This data was used to create a dichotomous variable that was equal to one if the state allowed s some level of controlled substance prescriptive authority and zero if it did not for each year.
Table 2 provides a snapshot of the number and percent of states authorizing s to prescribe controlled substances by year, from 1991 to 2003. As can be seen from Table 2, there was a significant change in the proportion of states that authorized s to have controlled substance authority. This variation in state practice authority makes the time period ideal to investigate.
The results of the regression estimations can be found in Table 3. For the probit estimation, the marginal effects are reported since probit coefficient estimates are not directly interpretable. The interpretation of the marginal effect coefficient is the change in the probability of a move for an with the sample mean characteristics if there is a one unit change the independent variable in question.
All of the demographic variable coefficients are in line with expectations and most are statistically significant. Of most interest is that the estimated impact of state practice authority is negative and significantly different than zero at conventional significance levels. This is true for both the linear probability model and the probit model which provides some robustness check.
The interpretation is that an is less likely to move from a state that has granted expanded prescriptive authority than if the state had not, controlling for other influences. Not only is the effect statistically significant, it is also material. The point estimate from both estimates is approximately −0.03. This implies that if a state has granted s expanded prescriptive authority, the probability of an average moving from the state falls by roughly three percentage points. Considering that on average about 6.5% of s in the sample moved in a given year, a state authorizing expanded authority to s leads to a reduction in the probability of moving of around 46%. This implies that the level of authority a state grants to s is meaningful to locational decisions.
It is also informative that the estimation results are robust to changes in specification and sample. The estimated results are materially unchanged when age restrictions and/or demographic variables are changed or omitted. The robustness of the empirical estimates provides some assurance that the effect of expanded prescriptive authority being measured is real.
There are weaknesses in the current research that should be acknowledged. Of particular note, while the NSSRN has high level of detail on an individual , the information is for the specific survey year. For example, the 2004 NSSRN data asks the respondent about the status in 2004 of most variables, such as income and marital status. Since the NSSRN asks where the was in the previous year, the the data allows us to “see” what state the lived in 2003 which in turn allows us to see an move. Unfortunately, we do not “see” many other variables of note in 2003. This limits the controls that can be included in the regression. Most of the independent control variables that were included are variables that can be known or inferred from year to year (sex, age, race). Marital status and whether the has a child at home were also included in the final specifications even though they are reported only in the current year and not the previous year. That the coefficient estimates are as expected and the model is robust to whether these demographic variables are included are not provides some reassurance that the measured impact of authority is valid and not adversely impacted.
There is also the limitation as to the measure of state practice authority. Whether or not a state allows s to prescribe controlled substances was the measure employed but there are a number of reasonable approaches to measuring a state’s practice environment. However, there is no definitive measure. The current measure is commonly used in the literature as well as intuitive, tractable and represents a clear measure of difference between states as to what s are authorized to do as caregivers. It is not, however, a perfect measure of authority.
This research provides the first broad, microlevel analysis of the impact of state-regulated practice authority changes on individual s’ migration choices. The core finding is that an in a state that has granted expanded practice authority as measured through controlled substance prescriptive authority is less likely to move than if the state had not granted such authority. This finding is robust to specification and estimation technique.
This finding is in line with the macrolevel literature that finds a positive correlation between expanded practice authority and populations. In fact, it strengthens the macrolevel literature by providing a likely mechanism for which populations of s can change between states in response to state-level regulatory changes. Coupled with the research literature on quality and cost of care, which generally finds s provide care clinically similar to same-level physician-provided care, the results are informative to policy makers interested in the effects of regulatory changes on practice authority on the health care industry. This research also suggests that for regulated occupations, which include nearly all medical occupations, regulation changes of practice authority can materially impact individual behaviour.
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