Research productivity in neurosurgery: trends in globalization, scientific focus, and funding

A review

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While research is important for the survival, growth, and expansion of neurosurgery, little work has been done to quantify the status and trends of neurosurgical publications. The purpose of this bibliometric study was to quantitatively analyze trends in neurosurgical publications, including changes in worldwide productivity, study methodology, subspecialty topic, and funding.


This was a retrospective bibliometric study using MEDLINE to record all publications between 1996 and 2009 by first authors affiliated with neurosurgical departments. Country of origin, MEDLINE-defined methodology, study topic, and funding sources (for US articles) were recorded. Linear regression was used to derive growth rates.


Total articles numbered 53,425 during the study period, with leading global contributors including the US with 16,943 articles (31.7%) and Japan with 10,802 articles (20.2%). Countries demonstrating rapid growth in productivity included China (121.9 ± 9.98%/year, p < 0.001), South Korea (50.5 ± 4.7%/year, p < 0.001), India (19.4 ± 1.8%/year, p < 0.001), and Turkey (25.3 ± 2.8%/year, p < 0.001). While general research articles, case reports, and review articles have shown steady growth since 1996, clinical trials and randomized controlled trials have declined to 2004 levels. The greatest overall subspecialty growth was seen in spine surgery. Regarding funding, relative contribution of National Institutes of Health (NIH)–funded publications decreased from 30.2% (290 of 959) to 22.5% (356 of 1229) between 1996 and 2009.


Neurosurgical publications demonstrate continued increases in productivity as well as in global expansion, although US contributions remain dominant. Two challenges that the neurosurgical community is facing include the preponderance of case reports and review articles and the relative decline in NIH funding for US neurosurgical publications, as productivity has outpaced government financial support.

Abbreviations used in this paper: ISI = Institute for Scientific Knowledge; JIF = journal impact factor; MeSH = Medical Subject Heading; NCI = National Cancer Institute; NCRR = National Center for Research Resources; NHLBI = National Heart, Lung, and Blood Institute; NIA = National Institute on Aging; NIH = National Institutes of Health; NINDS = National Institute of Neurological Disorders and Stroke; RCT = randomized controlled trial.

Article Information

* Drs. Hauptman and Chow contributed equally to this work.

Address correspondence to: Jason S. Hauptman, M.D., Ph.D., Department of Neurosurgery, David Geffen School of Medicine at UCLA, 18-228 NPI, Box 957039, Los Angeles, California 90095-7039. email:

Please include this information when citing this paper: published online August 26, 2011; DOI: 10.3171/2011.8.JNS11857.

© AANS, except where prohibited by US copyright law.



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    Top producers of neurosurgical publications in terms of contribution to the entire neurosurgical canon. A: Thirteen-year trend in country publication records in terms of percentage of all neurosurgical literature. In the 1st year of the study period, the total number of neurosurgical articles indexed was 2840. At the end of the study period, the total number of neurosurgical articles indexed was 4796. The US has consistently produced between 30% and 40% of the global neurosurgical literature, remaining dominant in total neurosurgical publications despite rapid growth in global neurosurgical productivity over the study period. Germany and the United Kingdom have produced between 5% and 10% of global neurosurgical publication output. Japanese contributions to the global neurosurgical literature have been declining since the later 1990s, while Chinese production has been increasing primarily over the past 3–4 years. B–F: Top contributors to global neurosurgical publications according to publication type.

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    The top 20 countries contributing to the neurosurgical literature with the average JIF broken down by article type.

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    Growth of neurosurgical publications in the top 10 producers adjusted by 1996 levels. A: Among the top 5 producers, only China has been experiencing rapid, exponential growth over the past 10 years. The US, Japan, Germany, and the United Kingdom have remained relatively static in intrinsic publication output. The US and Germany have nearly identical publication growth rates, and therefore overlap. B: The next 5 top producers have all undergone consistent growth in publication output since 1996, most markedly noted in South Korea, Turkey, and India.

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    Growth of the entire neurosurgical canon according to publication type. A: Increases in review articles have outpaced all other types of journal articles. Case reports have also expanded at a greater rate than general neurosurgical research articles, keeping pace with overall productivity. B: Trend in all clinical trials since 1996. Numbers of clinical trials increased from 1996 and peaked in 2005–2006. Since then, clinical trial numbers have undergone a steady decline. C: Randomized controlled trials have undergone a similar trend as all clinical trials. Currently, RCT numbers are in a decline, and in 2009 they approached levels of 5 years ago.

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    Growth in papers categorized by MeSH. Note that for Vascular, 2 populations are displayed: all papers labeled with MeSH terms specific for vascular neurosurgery and papers labeled with MeSH terms specific for endovascular neurosurgery. Similarly, for Functional, all papers with MeSH terms for functional neurosurgery are displayed as well as a subpopulation of papers labeled with MeSH terms specific for deep brain stimulation (DBS).

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    Changes in identified funding sources for US neurosurgical publications. A: The top 5 branches of the NIH that are identified sources of funding for neurosurgical research include the NINDS, NCI, NHLBI, NIA, and NCRR. B: The number of publications with stated NIH funding have remained relatively constant, while the number of non–NIH-funded (unfunded) publications are rising. C and D: The NIH-funded US publications by methodology. E: Comparison of growth of total US publications and those with stated NIH funding. F: Journal impact factors for publications with stated NIH funding compared with overall US neurosurgical publications.



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