Abstract
Aim
This study charts the growth of the scientific journal literature on headache for 30+ years (1983–2014).
Methods
Using the Web of Science, articles published in four two-year periods (1983–1984, 1993–1994, 2003–2004, 2013–2014) from journals indexed in the Science Citation Index Expanded database were retrieved and analyzed.
Results
From 1983–1984 to 2013–2014, the scientific literature on headache increased nearly fourfold (3.8) from 468 to 1776 articles; the number of participating countries more than doubled (26 to 67); and the two most prolific countries in each period were the USA and Italy. While several European countries (Italy, Germany, UK and Denmark) were among the top 10 in each period, the notable appearance of Turkey, China and Brazil among the top 10 in 2013–2014 indicates the growing geographic spread of publications on headache research. Meanwhile, the comet-like distribution of journals has not changed: two journals, Headache and Cephalalgia, persist throughout as the nucleus, with the tail increasing more than threefold from 141 journals in 1983–1984 to 462 in 2013–2014.
Conclusion
Our study follows the recent growth and spread of the scientific literature on headache research and should stimulate further bibliometric investigation in this field.
Introduction
Based on historical and legendary reports (1–3), headache has been with man since its early history. Notions on headache symptoms have been evolving from antiquity through the 19th century (4), and continue into the 20th century along with clinical and scientific observations (5).
During the last decade, headache disorders in the general population have been regularly assessed: for example, a recent WHO report indicated that “globally, it has been estimated that prevalence among adults of current headache disorder (symptomatic at least once within the last year) is about 50%” (6), while another report (7) revealed that the headache years lived with disability (YLD) is nearly the same as the disability adjusted life years (DALY). These data show the importance of headache disorders in the population; it also confirms that, despite numerous investigations in the last decades, headache treatment has not yet been achieved.
Although numerous review papers are regularly published, providing qualitative information on the development of headache research aimed at the scientific and medical communities, to our knowledge only a few reports have charted its literature growth. Published more than 15 years ago, Norton and his colleagues (8), examined publication trends in chronic pain, including chronic headache. However, as headache-related research was not separated from general pain research, no comparison of their data could be used in our study. In a Chinese paper with only an English abstract, Zhang and his colleagues (9) investigated the “distribution and hot spots of literatures on headache by bibliometric analysis in order to provide reference for further study”.
The objective of this paper is to give a quantitative description of the medical and scientific literature on headache research published during the last 30+ years. The following parameters are discussed: number of publications and contributions by countries, and journals. Additionally, we hope that it will motivate readers to extend this brief overview with further bibliometric investigations to provide useful information to headache researchers, medical and scientific researchers, clinicians and funding organizations.
Methods
The data were collected in February 2016 from the Science Citation Index Expanded, a multidisciplinary index to the journal literature of science and technology, through the ISI Web of Knowledge™ (http://www.isiwebofknowledge.com/).
The search strategy consisted of:
All articles published in journals with at least one of the following keywords in the title: migrain*, cephalalgi* or headache* with asterisks replacing characters following the word-stems; All articles published in the three journals Headache, Cephalalgia, and Journal of Headache and Pain.
After excluding duplicate documents appearing in both sets, only journal article-type papers published during the four time periods (1983–1984, 1993–1994, 2003–2004, 2013–2014) were downloaded for analysis.
For the top most prolific journals of the periods 2003–2004 and 2013–2014, the 2004 and 2014 impact factors (IFs) were collected using the Thomson Scientific Journal Citation Reports (http://scientific.thomson.com/products/jcr/). Documents were then sorted by countries and the number of articles authored or co-authored by researchers in each country was analysed; publications issued from more than one country were assigned equally to each contributing country.
Microsoft Excel was used to manipulate the data sets; publications originating from England, Wales, Scotland, and Northern Ireland were assigned to the United Kingdom (UK), and the European Union (EU) was defined as follows: 15 official member States from 1 January 1994; 25 official member States from 1 January 2004; and 28 official member States from 1 January 2014. The set of BRICS countries includes Brazil, Russia, India, China, and South Africa, while the set of 11-next countries includes Bangladesh, Egypt, Indonesia, Iran, Mexico, Nigeria, Pakistan, Philippines, South Korea, Turkey, and Vietnam.
Results
Country distribution of headache scientific article-type papers for four periods: 1983–1984, 1993–1994, 2003–2004 and 2013–2014.
Countries publishing headache research
Table 1 shows that during the four two-year periods we studied, the number of countries participating in headache research more than doubled: there were 26 participating countries in 1983–1984, 34 in 1993–1994, 58 in 2003–2004 and 67 countries in 2013–2014. Countries were ranked in decreasing order of productivity (number of papers) for each two-year period. In all four periods, the USA was the most productive country, followed by Italy. The percentage share of publications from the USA increased during the first three periods (23.9% in 1983–1984, 33.7% in 1993–1994, 36.3% in 2003–2004), then decreased in the last period (29.1% in 2013–2014). Italy’s share of publications throughout remained relatively constant from 11% to 15.2%. Throughout the four periods, the UK and Germany were in the top four most productive countries. Three countries (Turkey, China and Brazil) emerged as top contributors in headache research. Turkey first appeared with only two papers in 1993–1994, ranked 6th with 53 papers in 2003–2004 and then ranked 5th with 108 papers in 2013–2014. China had five papers in 1993–1994 and two papers in 2003–2004; however, it moved to rank 6th in 2013–2014 with 92 papers. Brazil appeared in 2003–2004 with 40 papers (rank 10th) and then moved to rank 9th with 67 papers in 2013–2014. When results are viewed globally, we see that the EU increased its share from 1993–1994 (37.1%) to 2003–2004 (50.3%), but then declined in 2013–2014 (41.3%). The BRICS countries and the 11-next countries showed similar trends: during the 2003–2004 period, their productivities were similar (65 and 67 papers respectively, each representing 5% of all publications on headache research); however, both country groupings increased threefold in the last period (2013–2014) with 198 and 216 papers respectively, representing 11.1% and 12.1% of all headache-related publications during 2013–2014.
Journals publishing headache research
Top most productive journals in headache research during the four periods: 1983–1984, 1993–1994, 2003–2004 and 2013–2014.
During the last two periods the mean impact factor (IF) of the top 10 journals increased from an average of 1.92 (2003–2004) to 3.40 (2013–2014): in 2003–2004, 6 journals had IFs <2; while only 3 journals had IFs <2 in 2013–2014 (see Table 2).
Discussion
The major findings of the present study on the evolution of the headache scientific literature during 1983–2014 are: the nearly fourfold (3.8) increase in the number of publications from 1983–1984 to 2013–2014; and the spread and distribution of papers among publishing countries from 26 in 1983–1984 to 67 in 2013–2014.
Limitations of the methodology
By using only the Science Citation Index Expanded from the Web of Science our study is limited to articles primarily in the major journals of science and technology (including medicine). Quick searches in other databases such as PubMed, Google Scholar and Scopus retrieved more journal papers (from more journals indexed); however, each database has advantages and drawbacks when compared to the Web of Science for scientific and/or medical literature (10). We chose the Web of Science as it remains the database generally chosen by information scientists for bibliometric analysis – especially for studies spanning many decades and requiring reasonably “clean” and accurate data.
Another possible limitation is our search strategy which restricted headache-related keywords to only the titles of journal papers. This option was chosen in order to avoid possible retrieval of irrelevant articles if other subject-related fields such as abstracts or keywords were included; titles are generally terse and carefully worded by authors to reflect the focus of the paper.
The inclusion of all articles in the journals Headache, Cephalalgia, and the Journal of Headache and Pain, regardless of whether headache-related terms appear in the titles, is justified by the fact that the vast majority of the articles published in these journals are headache or face pain-related. Our analysis is based on documents published as articles, excluding editorials, reviews, or technical notes. This choice was made in order to retrieve only publications that contain the core of research on headache. We did not include Opinion Series and Expert Series as we wished to focus on the major peer reviewed journals. As a consequence of these choices, we likely underestimated the real volume of research performed on headache. However, we are convinced that our data provide pertinent and useful description of the headache research literature.
Evolution of productive countries
USA
Over the study period (1983–2014) the USA was by far the most productive country (Table 1). If the share of USA publications remains at a high level in all four periods (23.9% for 1983–1984; and 33.7%, 36.3% and 29.1% respectively for successive periods), the decline in 2013–2014 is in line with forecasts by USA-based science policy analysts (11).
The contributions of the USA scientific and medical headache research communities were recently summarized (12), and in their decade-by-decade (1950s to 2000s) report Solomon and his colleagues document trends, ideas, and changes in the USA, including, for example: legitimizing the terms ‘headache’ and ‘migraine’, forming the American Association for the Study of Headache (AASH), later renamed the American Headache Society (AHS) and launching the journal Headache in the 1950s and 1960s; developing headache clinics in the 1970s; introducing Triptans at the end of the 1980s; and developing imaging technologies to investigate headache mechanisms in the 2000s. More recently, Headache Medicine has become a legitimate subspecialty with a board certification process (https://www.ucns.org/go/subspecialty/headache).
Unfortunately, there has been a significant underfunding of research on headache disorders in the past decade as highlighted by Shapiro (13). Schwedt and Shapiro (14) report on 2007-NIH funding of headache disorders vis-à-vis other disorders: $13 million for headache disorders while funding for 10 other comparable disorders ranged from $98 million to $1.04 billion; in 2012-NIH funding, $18 million went to research for migraine versus $156 and $154 million for epilepsy and Parkinson's disease, respectively (15). Apparently the underfunding of USA institutions for headache research still has not been addressed.
Italy
Italy is ranked 2nd in number of papers published in all four time periods during 1983–2014. This is not surprising as Italy has had a long and active tradition in neurological and neuroscience research (16,17). The important contribution of Italy to headache research during these last decades was highlighted 10 years ago (18). Additionally, the reader is reminded that Neurological Sciences (formerly the Italian Journal of Neurological Sciences) is the official journal of the Italian Neurological Society and of the Italian Society of Clinical Neurophysiology.
Germany
During the last two periods (2003–2004 and 2013–2014), Germany ranked 3rd in the number of publications and ranked 4th in the earlier two periods (1983–1984 and 1993–1994); it increased its number of publications fivefold from 28 in 1983–1984 to 146 in 2013–2014. The established presence of the German scientific community in the field of headache research is further illustrated by a publication (19) on migraine attacks which has been cited over 1200 times according to Google Scholar (https://scholar.google.ca/). According to Straube and Gaul (20), German headache research started partly through the efforts of Soyka and the founding of the German Migraine and Headache Society (DMKG) in 1979 and several years later in 1982, the founding of the International Headache Society (IHS) congress in Munich. A further development is the establishment of “integrated headache centers” that offer multimodal treatment of headache disorders. Finally, four German-language journals (Medizinische Welt, Nervenheilkunde, Nervenarzt, and Schmerz) are among the top journals in headache research.
UK
The ranking of the UK among the most productive countries in headache research has been relatively constant over the four periods: 3rd in 1983–1984 and 1993–1994 and 4th in 2003–2004 and 2013–2014; its scientific literature more than doubled (49 papers for 1983–1984 and 110 for 2013–2014). The importance of the UK in the field of headache research can be shown through the launching of the Migraine Trust in 1965 (21), with its accompanying meetings: the first Migraine Trust International Symposium meeting was held in 1976, and the next meeting, referred to as the 5th European Headache and Migraine Trust International Congress, will be held in Glasgow in 2016 (http://ehmtic2016.com/).
Turkey
While publications by Turkey’s researchers only started appearing in 1993–1994, Turkey quickly increased its presence in the 21st century by joining the top 10 most productive countries in 2003–2004 with 53 publications and doubling its output in 2013–2014 with 108 publications (Table 1). To accompany this significant increase in research publications, Turkey continuously participates in the international headache community by hosting headache-related congresses: the 6th Headache Congress in 2002 held in Istanbul; the 1st Turkish-African Meeting of Headache and Pain Management in 2015 (http://www.tahpm.org/); and the future organization of the 19th IHS Congress in 2019.
China
China experienced a meteoric rise in productivity from only five and two papers in 1993–1994 and 2003–2004 respectively, to 92 (ranked 6th) in 2013–2014 (see Table 1). Using linear extrapolation of future publication trends based on Scopus, The Royal Society (22) predicted China surpassing the USA in total number of publications by 2013. A quick search on Scopus shows that in 2013 the USA still leads China in total number of article-type publications in all fields; however, by 2015 China had narrowed the gap considerably. Leydesdorff (23) states that “China no longer grew exponentially during the 2000s, but linearly” and therefore the “cross-over of the lines for China and the USA is postponed to the next decade (after 2020).”
Denmark
Over the four periods (1983–1984, 1993–1994, 2003–2004, 2013–2014), Denmark consistently ranked among the top 10 productive countries (Table 1) in headache research despite its small population (5.6 million in 2013–2014). Indeed, since the end of World War II, Denmark played a major role in the development of headache research (24).
Brazil
A 2015 special issue of the journal Headache on “the Brazilian contribution to the diagnosis and treatment of headache disorders”, leads with an historical overview of headache research and medical practice in Brazil (25). Brazil’s influential neuroscientist Leão identified cortical spreading depression phenomenon and was first to suggest the possibility of its connections with migraine (26). Since the formation of the Brazilian Headache Society in 1978 and the creation of its journal (first only accepting papers in Portuguese and later renaming its journal, Headache Medicine, to attract papers in both English and Portuguese), headache research in Brazil took off. Although Brazil did not appear as a contributor of papers in the first two periods (1983–1984 and 1993–1994), it ranked 10th with 40 papers in 2003–2004 and 9th in 2013–2014 with 67 papers (Table 1). Finally, the rapid progression of Brazil’s productivity was also observed in the field of pain research which is closely related to headache (27).
EU member states
Since the 1993–1994 period, the EU has been the most prolific country-grouping in headache research. Globally, the EU-27 in 2010 had the most number of publications (ranked 1st) across all fields in both the Web of Science and Scopus databases when compared with the USA, ranked 2nd and China, ranked 3rd (23). However, in 2013–2014 the productivity of the EU-28 declined to 41.3% after capturing slightly over one-half (50.3%) in the previous period, 2003–2004 with fewer member States (EU-25).
Nevertheless, the importance of the EU in the field of headache research is illustrated by the presence of journals created in EU member States: for example European Journal of Neurology, Revista de Neurologia, European Neurology, Schmerz, etc. Furthermore, in the 2013–2014 period eight EU countries were among the top 15 countries publishing from 59 to 237 papers; another nine EU countries contributed from five to 35; and six EU countries published from one to three papers. Variation between EU countries is also seen regarding the burden and cost of headache diseases as revealed in a recent report (28). Homogenization of health policies should help to diminish this socio-economic consequence of headache. Finally, as in the USA, EU headache research also has financial difficulties (29). If some of the above concerns are addressed, headache research in the EU should improve.
BRICS and 11-next countries
One important result of our study is the arrival of new actors belonging either to the BRICS (Brazil, China) or to the 11-next countries (Turkey). Although both country groupings more than tripled their productivity from 2003–2004 to 2013–2014, global analysis is hampered by their heterogeneity – geographic spread, population size, political persuasion, etc. (30) and by the diversity in their education and scientific profiles (31).
African countries
The scant involvement of African countries in headache research observed in our study is illustrated by the small number of African countries publishing in this field (two in the earlier three periods and six countries in 2013–2014), and by the small number of headache-focused papers published by each of them (≤5). Woldeamanuel and his colleagues (32) provided an interesting synthesis of a 43-year epidemiological investigation in migraine headache in Africa, indicating that “recent studies further indicate a rapid increase in migraine prevalence within the coming decades”. Added to the population explosion forecast, and to the state of neuroscience research in this continent (33), developing headache research in Africa is an important and urgent challenge.
Headache journals
The more than threefold increase in the number of journals publishing headache research (143 in 1983–1984 vs 462 journals in 2013–2014), parallels the comet-like distribution of papers in journals: for the 2013–2014 period, a core or nucleus of a few (<5) journals published almost 40% of the papers, followed by a long tail of journals publishing the remaining headache-related papers (see Results section). The core journals specifically dedicated to headache-related papers are: Headache, Cephalalgia, and Journal of Headache and Pain; Cephalalgia, launched in 1981, is the official journal of the International Headache Society and has the highest IF of the three. However, two non-headache journals were extensively targeted by headache researchers (Neurology for the periods 1993–1994 and 2003–2004, and Neurological Sciences for the periods 2003–2004 and 2013–2014). In 2013–2014, eight papers dealing with headache research were published in prestigious medical journals with IFs >15. Additionally, the journal Lancet Neurology provides several pages in the first issue of each year highlighting the previous year’s progress in headache research.
International trends in headache research influencing publishing
Several international trends influencing the publishing of headache research include: (1) the launching of Triptans in the early 1990s, currently the most widely used treatments for moderate-to-severe migraine headaches (34); (2) the publication of multiple issues of the International Classification of Headache Disorders supported by the IHS (http://www.ihs-headache.org/ichd-guidelines) and spearheaded by Olesen; the 1988, 2004 and 2013 versions of the classification are both summaries of the state of knowledge and a powerful motive for research to test new ideas in classification; and (3) the development of “Lifting the Burden”, the global campaign against headache, in official collaboration with WHO, led by Steiner (35) who summarizes three stages: “Acquiring knowledge for action, using knowledge to raise awareness, and exploiting awareness to promote beneficial change.”
Conclusion
The last decades (1983–2014) witnessed the growth of publishing activities in headache research. During this period the geographic landscape of the field expanded from an initial 26 countries in 1983–1984 to 67 participating in 2013–2014. Although historically contributing countries (USA, Italy, UK, and Germany) remain leaders in headache research, newcomers (Turkey, China, and Brazil) are rapidly joining the top 10 productive countries in the field. Future bibliometric analysis could focus on more specific subfields such as: headache triggers; headache therapeutics; and intrinsic headache mechanisms. An extension of literature coverage could include other databases such as PubMed and Scopus along with country-specific databases such as SciELO (Scientific Electronic Library Online of Brazilian journals) and CSTPC (China Scientific and Technical Papers and Citations).
Footnotes
Article highlights
From 1983 to 2014:
The scientific literature on headache increased nearly fourfold; The number of headache publishing countries went from 26 to 67; The number of journals publishing headache research more than tripled. Currently: The most publishing countries are: USA, Italy, Germany, UK, and China; Almost 40% of the headache literature is concentrated in five journals.
Note
Part of this work was presented at the 8th European Neurology Congress, Amsterdam, Netherland, 21–23 September 2016.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.