Economic burden of Parkinson’s disease and research trends: a bibliometric analysis

Countries

Table 1 shows the countries scientific production, based on the affiliations of all authors of each article, of the documents analysed in this work. The 140 articles analysed here came from 34 countries, of which 58.8% were from European countries, whereas 20.6% were from Asia, and 11.8% from the USA. However, the most productive country was the USA with 113 (80.7%) articles, followed by the UK with 87 (62.1%) articles and Germany with 73 (52.1%) articles. The countries that contributed the least were Brazil, Greece, Iceland, Ireland and Switzerland with 0.7%.

Table 1 Countries scientific productionAuthors and affiliations

The articles included in this study were written by 736 researchers. Furthermore, the average number of co-authors per article was 6.69. A total of three articles (2.1%) were written by a single author, while a total of 137 articles (97.9%) were written by multiple authors. Furthermore, the analysis of the articles revealed that the 10 most relevant authors for the topic in question were the authors described in Table 2. This table shows the h-index – a common metric for evaluating the scientific merit – the year of publication of the articles and number of articles published. As described, Oertel Wolfgang and Dodel Richard had the highest h-index among the 736 authors and were also the most prolific authors with the largest number of publications and citations. More specifically, Oertel Wolfgang had an h-index of 11, 13 publications and 587 citations. On the other hand, Dodel Richard had an h-index of 10, also 13 publications and 505 citations. It is noteworthy that Dodel Richard also appears in the top 10 most relevant authors under a different name, Dodel RC. Dodel RC has an h-index of 4, 5 publications and 216 citations.

It is worth noting that it is also important to understand the connection of these authors with affiliated organizations in the production of scientific knowledge (Supplementary material 1), as these institutions help in the dissemination and expansion of knowledge. The four most relevant institutions affiliated with the authors of the selected studies are Radboud University Nijmegen with 20 articles as the most relevant institution, followed by University of Marburg with 17 articles and both King’s College London and University of Bonn with 11 articles each.

Journals

The most productive journals on economic burden in PD are listed in Table 3. As can be seen, the top three journals are Movement Disorders (27), Parkinsonism & Related Disorders (13) and Pharmacoeconomics (13). Most of the journals are included in one or two categories, with Clinical Neurology and Neurosciences being the top two. This suggests that these categories exerted a major influence on the economic burden of PD and that it is a specific field. Lancet Neurology has the highest impact factor (48.0) and Movement Disorders has the highest number of citations (1995) with 27 articles published on this topic.

Table 3 Top 20 journals with the most published literature on economic burden in PD

The annual growth rate of published articles was 57%. As shown in Fig. 2, the analysis of journal production over time revealed that the number of articles published in the three main journals mentioned has increased in recent years. Furthermore, Movement Disorders is the journal with the highest growth, followed by Parkinsonism & Related Disorders and Pharmacoeconomics.

Fig. 2figure 2

Journals production over time

Citations

The 140 articles were published in 41 different scientific journals, with an average citation rate of 37.97 per article. The most cited articles are listed in Table 4. The first is from Kowal and colleagues (Kowal et al. 2013) with 447 citations and the second is from Huse and colleagues (Huse et al. 2005) with 225 citations. Both articles estimate the economic burden of PD in the USA and the third article by Findley and colleagues (Findley et al. 2003) with 170 citations, also estimates the economic burden of PD but in the UK. These three top articles were published in the most prolific journal on the subject, Movement Disorders.

Table 4 Most global cited documents on economic burden in PDThematic map and co-occurrence network

Figure 3 presents a thematic map in which each of the circles represents a cluster of research topics. In this map, the X-axis represents centrality, which measures the intensity of the links between the clusters – clusters with numerous and stronger links mean that they denote a set of research problems that are considered crucial by the scientific community. Density, on the other hand, is plotted on the Y-axis and measures the degree of development, i.e. the strength of the links that exist between the words that make up the cluster. Stronger links mean that the research problems form a coherent and integrated cluster. Therefore, this map classifies a research topic into four quadrants based on these two values, each representing a specific topic module. The thematic map is interpreted by analysing where the keyword or research topic is located. Moreover, the size of the circle represents the size of the cluster, i.e. the number of research topics/keywords it contains. Large circles represent research topics of greater importance and small circles for research topics of lesser importance.

Fig. 3figure 3

The results show that there are two clusters with high centrality and density in the first quadrant, “double-blind, safety, long-term” and “therapy, bromocriptine, multicentred”. These clusters focus on items related to PD and are the topic of motor research.

In the second quadrant there is a cluster with high density that represents niche themes “balance, index, physiotherapy, performance”, while the third quadrant consists mainly of three clusters representing emerging or declining themes: “metanalysis”, “fall” and “disability”.

The fourth quadrant consists of three clusters with low density, but high centrality, i.e. the basic themes: “entacapone, health, United States”; “dementia, depression, diagnosis” and “validation, disease, questionnaire”. Finally, the cluster “quality-of-life, impact, illness” that is located between the first and fourth quadrant has a high level of centrality and moderate density but has the largest cluster frequency given its size.

The map of co-occurrence of themes analyses in a complex way the themes of the studies that occur simultaneously between the authors and is included in supplementary material 2. The map shows that the most frequently occurring themes are “quality of life”, “impact” and “illness”.

Keywords

To answer the first question of the study – “What are the main keywords regarding cost research in the area of Parkinson’s disease? – the results show that the authors wrote 140 articles with more than 320 keywords. The most important words are listed in Table 5. The words are presented in order of relevance, with “quality of life” as the most relevant, with 49 (35%) occurrences, and “economic burden” ranked 6th position out of 25 words, with 18 (12.9%) occurrences. The use of keywords plus in bibliometric analysis is more effective to investigate the knowledge structure in scientific fields as they offer several advantages due to their large number of concepts and broad meaning (Zhang et al. 2016).

Table 5 Top 25 most relevant words

Figure 4 displays a word cloud to help to quickly understand the most relevant terms, such as “quality-of-life”, "impact" and “illness”.

Fig. 4figure 4Lotka’s Law and Bradford’s Law

The results of the bibliometric analysis for the question—“How do an author’s studies on the economic burden and costs of Parkinson’s disease influence scientific production?” – can be seen in Tables 6 and 7, which show the results of the bibliometric analysis based on Lotka’s Law (Lotka 1926) and Bradford’s Law (Bradford 1934), applied to the sample of the present work, supporting the interpretation of question 2 of the study.

Table 7 Bradford’s Law

Lotka’s inverse square law of scientific productivity, also known as Lotka’s law, determines the productivity of authors within specific research areas and is used to assess the frequency with which authors publish articles (Coile 1977; Potter 1981). The more articles published, the less frequent the authors who write these publications become. As in this research analysis, more than 80% of the authors (629) published one article, while only 3% of them (2) published 13 articles. Table 7 presents the results of the Bradford’s Law.

According to Bradford’s Law, the first articles on a new topic are submitted to a small selection of suitable journals. If these articles are accepted, these journals attract further articles as the subject area develops (Brookes 1969). This phenomenon is known as the “mechanism of success generating success”. If other journals publish their first articles on the topic at the same time and the topic continues to develop, a core of journals will eventually emerge that corresponds to the most prolific journals in terms of articles on that topic. Our research has shown that Movement Disorders, Parkinsonism & Related Disorders and Pharmacoeconomics are the most important sources.

Finally, Fig. 5 shows the average annual scientific production on the topic of the current work, which is essential, as it not only informs us about the current state of scientific production on this very relevant topic but also helps us to understand the distribution over the years. Therefore, Fig. 5 presents a line with an oscillating pattern of fluctuations, however, with a peak of 15 published articles showing the highest production on this topic in 2021, followed by a slow decline in 2022 with 10 published articles. This shows a growing interest in this topic.

Fig. 5figure 5

Annual scientific production

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