Tendency and foci of nurse practitioners: bibliometric analysis based on the CiteSpaceV^†

The data of this bibliometric study came from the WoSCC database, which includes Science Citation Index Expanded, Social Sciences Citation Index, and Arts and Humanities Citation Index.

To explore the trends in NPs, we retrieved NPs-related studies published from 1986 to 2018 (as literature cannot be fully covered until 2019) in the WoSCC database. The index topics included “Nurse Practitioners,” “Nursing,” “Nurses,” “Practical,” and “Private Duty.” And the retrieval strategy is as follows: TS = (“Practical” and “Nurses”) OR (“Practical” and “Nursing Care”) OR “Nursing, Private Duty” OR “Nursing, Practical,” OR “Nurse Practitioners.” All studies were retrieved and downloaded on June 20, 2019. Simultaneously, the “fully documented and cited references” of literature were exported in the “other file formats” using the format of “plain text”. The types of documents downloaded are “review” and “articles” and no language-related restrictions were applied to the search. All the searched records were exported to CiteSpaceV software for further analysis, and then all results were organized using Excel 2016.

Not only the bibliometric analysis but also the visualization of literature is used widely to analyze the relevant research data in many research fields, such as psycho-metric, nanotechnology, aviation engineering, economic geography, ecological security and science, strategic management, and technology policy analysis.¹⁴ However, the bibliometric analysis about nurses, especially the NPs, still produced only sparse results. In order to explore more about the development tendency and hotspots in this field, the CiteSpaceV software has been used in the visualization related to NPs. CiteSpaceV is a software used in literature metrology. Using it, we can identify the literature and information visualization in many knowledge domains. It was developed by the team of Chaomei Chen of Drexel University, US, using Java program.¹⁵ The CiteSpaceV is inspired by Thomas Kuhn's structure of scientific revolutions that centers on the change of research focus over time, sometimes incrementally or rapidly. Recently, CiteSpaceV has also been used in medicine sometimes. However, the nursing-related articles are relatively few. There were only 546 published papers^{16, 17, 18} that were related to clinical nursing, nursing education, palliative care, and midwifery.

Based on what has been analyzed above, we made a bibliometric analysis of the literature on NPs using CiteSpaceV. Many visual items were used in our study, for example, (1) the analysis of citation and co-citation can help us to detect hot-topics in the field which we focus on; (2) although this metric—which can be found in every project—is burst, it is a normal one; however, it is very important to do a burst detection algorithm to identify emergent research-front concepts, reference and authors, and so on;¹⁹ (3) centrality is an important index of visual analysis, which can be used to measure and highlight the potential pivotal points in some research fields;²⁰ (4) in addition, through the analysis of author, country, and institutions, we can detect the one that is the pivotal-point, and that will be provided as the reference for us to get cooperation. The results of our study are as follows.

The initial search identified 4912 entries, including 4547 articles (92.57%) and 365 reviews (7.43%). Furthermore, it contains 15 languages, such as English (4802, 97.76%), German (30, 0.61%), and Portuguese (16, 0.33%); and English has the highest entries. Out of the 4912 studies, the first article on NPs was published in Belgium by De Becker²¹ in 2007 in a series of books, which are entitled Contributions to Nephrology, and the title of the paper is “Starting Up a Continuous Renal Replacement Therapy Program on ICU.” The latest one is a cohort study that was published in the US by the authors Jackson GL.²² The topic of this paper was “Intermediate Diabetes Outcomes in Patients Managed by Physicians, Nurse Practitioners, or Physician Assistants: A Cohort Study” in the journal Annals of Internal Medicine. We know that the number of studies in this field has increased rapidly from 2007 to 2018, especially in the recent 3 years (1698, 34.57%). The citation frequency of the papers shows the degree of influence. As we can see, the citation counts of NPs have been increasing fast, this being the case especially in 2018 (9083) (Figure 1). Overall, the publication tendency of papers is steadily increasing, and the citation count of these papers is increasing rapidly.

Figure 1

In this section, we analyzed the publication and citation frequency of authors and list the top 10, as shown in Table 1. As we can see, the high-productive author is Gardner G (24, 0.49%) in this research field according to the number of papers. In addition, the strength of the burst of Gardner G (burst 5.26, 2015–2018) ranked second among the top 10 authors (Table 1). This indicated or showed that Gardner G was the one who was involved in this research field in recent years and made a contribution to it. Both the citation frequency (464) and the citation frequency per paper (19.33) of Gardner G were more than others. However, based on the result we can get, the centrality of all authors was 0. It was apparent that no core authors group was formed.

If, in an article, 2 or more authors are from the same institute or country, it is referred to as cooperation. In this section, we will analyze the institutes and countries of the authors of these studies. Judging cooperation based on the co-occurrence frequency of institutions and countries, we found the top 10 institutions and countries. First, we must remember that the size of the circle indicates the number of papers published by institutions and countries. The thickness of links represents the linking strength between institutions or between countries. As we can see, the University of Michigan (90, 1.83%) is the most productive one among the 4557 institutions and the University of California, San Francisco (88, 1.79%) comes second (Table 2). From the centrality of institutions, we can see that Columbia University was higher than others. It was suggested that Columbia University obtained the key position in this field. The result based on countries was as follows: the US (2737, 55.72%) is a high-productive country among these 98 countries. It shows that the US and UK (398, 8.10%) (Table 3) did well and become more active in this research field. According to the knowledge map of institution and country (Figures 2 and 3), we can see that the links are too thin to show that the linking strength still needs to be reinforced in the future. And the institution named Radboud University Nijmegen was in a highly farther position from the others. It was shown that it lacks relations with others.

Figure 2

Figure 3

The analysis of journals can help us to find the effectiveness and provide a reference for us to choose the target journals. Results show that JAMA, a journal of the American Medical Association (IF = 47.661) is the most effective one which has counts of citation numbering around 1386, and the Journal of Advanced Nursing followed. Half-life of co-cited journals shows the duration of influence. In the top 10 co-cited journals of NPs, the following 3 journals own the highest half-life: Journal of Clinical Nursing (half-life = 8), International Journal of Neural Systems (half-life = 8), and Health Affairs (half-life = 8) (Table 4). The top 10 co-cited journals, arranged according to the strength of burst, shows that the journal PloS one has the strongest burst (burst = 41.35) (Table 5). Funding support can reflect the firm support of countries for some research fields. From Table 6, it can be seen that some funding institutions such as “Agency for Healthcare Research and Quality” (39, 0.79%), “National Institute for Health Research” (22, 0.45%), and “National Institutes of Health” (17, 0.35%) had supported many papers dealing with NPs compared to other grants. We not only pay attention to the frequency of funding support but also care about the half-life. Half-life brought out the significance of time-duration of grant support, which can be taken as a reference to researchers to obtain the necessary funding support to ensure that their project work proceeded well. Among the top 10 funding institutions the “National Institutes of Health” (half-life = 9), “National Institute on Aging” (half-life = 9), and “Canadian Institutes of Health Research” (half-life = 9) provided continuous support in this field. In addition, their support frequency is also very good.

The analysis of the co-cited references, especially the citation burst, can show a significant increase in the fields in which researchers are interested. This study listed the highest citation count references and their strength of burst from 2007 to 2018 and formed a knowledge map (Table 7, Figure 4). The paper “The Role of Nurse Practitioners in Reinventing Primary Care” ²³ owns the highest citation counts with 72, and was written by Naylor MD, 2010. It was published in the journal Health Affairs (Table 7). In this paper, the author has summarized enough evidence to demonstrate that the NPs contributed to improving primary care and reduced more costly health resources. And the researcher recommended that nurses’ practice should be standardized and the performance results should be publicly reported. The objective of this study is to maximize the high-quality care provided by NPs. There is no centrality in the result of co-cited reference analysis, which revealed that they may not have formed the most key document in this research field and that higher-quality studies should be done in the future of NPs. As we can see, the article which has the most strength burst of co-cited reference is “Systematic Review of Whether Nurse Practitioners Working in Primary Care Can Provide Equivalent Care to Doctors” (burst 21.6, 2007–2009)²⁴ in the top 10 co-cited references (Table 7), which is a systematic review that detected whether NPs can provide care equivalent to doctors at the first point of contact in a primary care setting. Also, the researcher holds that although the patients are satisfied with the service of NPs as they are with doctors’ at the point of first contact, further research is needed to confirm that NPs’ care is safe in terms of detecting rare and important health problems.

Figure 4

Keywords can provide an insight into the main research topics in this research field clearly.²⁵ From Table 8 and Figure 5, we can see the top 10 keywords according to the occurrence frequency, which is not difficult to detect, are “nurse practitioner” (982), “care” (562), and “nurse” (555), which have the most occurrences. In addition to these, “primary care,” “education,” and “management” are more active in this field of study, and are capable of functioning as the hot-point at present or had done so previously.

Figure 5

We also analyze the burst strength of the keywords (Figure 6). The strongest burst may be a herald of the new direction in the progress of NPs. As the result shows, the “risk factor” (2010–2014) is the one that owned the highest burst strength, which is the new research point in this field, aimed at facilitating development progress. Furthermore, from “disease” to “diagnosis” is the new direction in this field, because their beginning time is late compared with others. Hence, this result can provide a reference to others who are interested in NPs.

Figure 6

From the overlay maps results, we can mainly analyze the knowledge transfer in this field.²⁶ As we can see, it is possible to discern a contrasting picture between the citing base map on the left and the cited base map on the right (Figure 7). As the result shows, there are 2 principal wire bundles, the one from “Medicine, Medical, Clinical” to “Health, Nursing, Medicine”, and the other one from “Psychology, Education, Health” to “Health, Nursing, Medicine.” We can draw a conclusion that the studies on the NPs have taken into account the clinical and nursing aspects, to be their references. Hence, if we continue to do research about NPs, we can pay attention in this direction.

Figure 7

Because the capacity of CiteSpaceV software for data is limited (10,000), there are some data do with the minimum spanning tree and pruning sliced networks. So, the data were simplified, and only then could they authentically reflect the level of development to some extent.