Bibliometrics of Vietnam Publications in the Science Citation Index: general trends and comparison with other tropical countries

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have been used to evaluate country publication performance, for example, six publication indicators such as total, independent, collaboration, first-author, corresponding-author, and singleauthor publications (Ho & Kahn, 2014); and citation indicators, for instance, total citations from Web of Science Core Collection since publication to the end of the most recent year (Wang, Fu, & Ho, 2011;Chuang, Wang, & Ho, 2011), citations in the most recent year only (Ho, 2012), and citations per publication (Fu, Wang, & Ho, 2012;Ho, 2018).
Located in Southeast Asia, Vietnam is the 15th most populous country in the world, with a mean yearly per capita gross domestic product of $ 8 000 and a medium human development index of 0.69; despite widespread poverty, the country's economy has grown significantly in recent years (Fforde, 2019).The Vietnam State Science Committee was established in 1959 with social, applied and basic science branches.In the early 1970s, scientific research facilities were also established in Nghia Do to cover Mathematics, Physics, and Marine Studies (vast.ac.vn).The 1980s were marked by close work with the Soviet Union, followed in 1993 by an emphasis on using high technological research for socio-economic development and more recently by the formal establishment of the Vietnam Academy of Science and Technology (vast.ac.vn, chinhphu.vn).
A study done a decade ago found that Vietnamese researchers were active in fields of pure and applied mathematics, theoretical and applied physics, public health and infectious diseases (Nguyen & Pham, 2011).A recent study reported that most Vietnam papers in the SCI are attributable to international collaboration, and that Vietnam is building up research capacity (Nguyen, Ho-Le, & Le, 2017).The country also has a growing academic interest in eco-compensation (Yu et al., 2020) and has good citation rates for Mekong River research (Sui, Chen, Lu, & Chen, 2015) and dengue research (Dwivedi, 2017), as well as patents for the printing industry, which show capacity for innovation (Kwon, Li, & Sohn, 2019).
The aim of this study was to analyze publications by Vietnamese researchers, in all fields of science covered by the Science Citation Index Expanded (SCI-EXPANDED) from 1991 to 2018, and to compare Vietnam with other tropical countries.

MATERIALS AND METHODS
The data refer not only to tropical biology, but to all areas of science covered by the Science Citation Index Expanded (last updated October 03, 2019).We searched for "Vietnam" in the country field, 1991 to 2018.The impact factors (IF 2018 ), used to compare the impact of different document types, and of locally-lead versus foreign-lead projects, were extracted from the 2018 Journal Citation Reports (JCR).
The database uses the term "reprint author", but here we use "corresponding-author".Single authors are considered both first-and corresponding-authors in this study.In documents with several "corresponding-authors" we used the last "corresponding-author".We used three citation indicators.The first was the number of citations from the Web of Science Core Collection in a particular year, for instance, C 2018 means the number of citations in 2018 (for a justification, see Ho, 2012).The second was total citations from the Web of Science Core Collection since publication to the end of 2018 was recorded as TC 2018 .The third was mean citations per publication (CPP 2018 = TC 2018 /TP).

RESULTS
Results are presented below according to type of publication, language, impact, subject and collaboration.Note: Figures 4-7, and Tables 3-9, appear as supplementary files in Digital Appendix 1 (figures) and Digital Appendix 2 (tables).
The maximal citations per publication value (CPP 2018 ) was in reviews with 34, which was 2.6 times the citation rate of common articles (Table 1).The mean number of authors per publication (APP) was 93 in data papers, 16 in articles and 9.2 in reviews (Table 1).Web of Science can classify a document in more than one type, for example, 1 332 proceedings papers were also classified as articles, and thus the sum of percentages can be higher than 100 %.We chose only journal articles (31 216 articles) for further analysis because they represented the majority of document types, as well as whole research ideas and results (Ho, Satoh, & Lin, 2010).

Publication output and citation impact:
The CPP 2018 increased more rapidly in the first year after publication.The initial value for citations per publication was 0.63 and reached a peak with CPP 2018 of 3.0 in the 2nd year (Fig. 1, Table 9 in Appendix 1).
The annual publication output and mean CPP 2018 for the years 1991-2018 appear in Fig. 2; they have increased steadily from 119 articles in 1991 to 4 992 articles in 2018; while the highest CPP 2018 was found in 2001 and 2004 with CPP 2018 of 31 for isolated articles produced by large international research projects.

Web of Science categories and journals:
To assess development among research fields and their interactions, we used a relationship between the number of articles in each category and publication year (Ho, Satoh, & Lin, 2010) (Fig. 4 in Appendix 2).The Vietnamese articles were published in 4 783 journals among all 178 SCI-EXPANDED categories.The top ten productive Web of Science categories are listed in Table 2, and Fig. 5 in Appendix 2.
The top 10 most productive journals are listed in Table 3 in Appendix 1 (Fig. 6 in Appendix 2).PLoS One (IF 2018 = 2.776) in the category of multidisciplinary sciences, published the most articles with 393 (1.3 % of articles).Articles published in Physical Review B and Journal of High Energy Physics had higher CPP 2018 of 18 and 17 respectively.In addition, articles published in Nature (IF 2018 = 43.070)had a CPP 2018 of 1 112.These tend to be journals that publish well financed research from large international projects, often in the fields of physics and medicine articles (Long, Huang, & Ho, 2014) with TC 2018 of 1 000 or more Koboldt et al. (2012) with TC 2018 of 4 577; Bhatt et al. (2013)
Neither the first nor the corresponding-authors of the most cited articles are Vietnamese, with a mean of 18 citations per publication (Fig. 3).
The top ten most collaborative countries are listed in Table 4 in Appendix 1 (Fig. 7 in Appendix 2).Vietnamese researchers collaborated the most with the USA including 3 949 internationally collaborative articles (13 % of articles).Nevertheless, Japan had the most first-and corresponding-author articles (7.1 and 7.6 %, respectively).Articles with Italy, the UK, and the Netherlands had higher citations per publication values (lower with South Korea and Japan).
A total of 3 898 (12 %) articles were single institution articles (IP) and 88 % were inter-institutionally collaborative articles (CP).Table 5 in    Citation life cycles of the most frequently cited articles: A total of 446 articles had a TC 2018 of 100, 52 % with a first-author from the USA (17 %), the UK (12 %), France (6.3 %), Japan (6.1 %), Switzerland (5.8 %), and Netherlands (4.5 %), while 50 % were published by a corresponding-author from the USA (19 %), the UK (13 %), France (7.2 %), Switzerland (5.8 %), and Japan (5.6 %).Table 7 in Appendix 1 shows the ten classic articles with a TC 2018 of 1 000 or more (Long et al., 2014).Nine had first-and corresponding-authors from the USA, in the tenth, they were from the UK.Eight articles were published by a big group with 357 to 774 authors.Furthermore, the Vietnam independent article with the highest TC 2018 (238 total citations) was "Expanding applications of metal-organic frameworks: Zeolite imidazolate framework ZIF-8 as an efficient heterogeneous catalyst for the Knoevenagel reaction" (Tran, Le & Phan, 2011)
Vietnam was colonized by France and for many years French was a second language in the country, but its publications in this database are 99 % in English, closer to countries like Gambia (Bah et al., 2019), Ghana (Boamah & Ho, 2018), and Brunei (Ho et al., 2018) which were colonized by the British.A probable reason is that journals covered by this particular index publish mostly in English.Other trends may occur in journals that publish in French or Vietnamese, but these are not covered by the index, even if they are important for the local development of research in Vietnam.In fact, the Science Citation Index Expanded is far from giving a representative view of science in Vietnam, because 95 % of all articles are published in Vietnamese and not covered by the index (Hien, 2010).
The increase in the number of publications, in all fields of science, is a general trend of tropical countries in the last decade, the same trend has been found in Asia (Ho et al., 2018), Africa (Boamah & Ho, 2018;Bah et al., 2019), and Latin America (Monge-Nájera & Ho, 2018;Calahorrano et al., 2020).
Vietnamese research published in collaboration with other countries was more cited in this database (CPP 2018 ) than local articles.Similarly, articles published by first-authors or corresponding-authors from Vietnam also had lower CPP 2018 values.For the 446 highly cited articles (TC 2018 100), 53 % had a first-author from the USA, the UK, France, Japan, Switzerland, or the Netherlands, while 50% were published by a corresponding-author from the USA, the UK, France, Switzerland, or Japan.International collaboration with developed countries produced higher citation rates.The USA contributed the most citations to Vietnam publications.The USA, Japan, South Korea, and France were the most frequent research partners.Collaborative articles with Italy, the UK, and Netherlands had higher citations.These patterns can be also found in other tropical countries (Monge-Nájera & Ho, 2017a;2017b;2017c;Tchuifon Tchuifon et al., 2017;Ho et al., 2018;Boamah & Ho, 2018;Bah et al., 2019;Calahorrano et al., 2020).
The reason for the importance of materials science research in Vietnam is that the subject was included as a priority by the government (Zink, 2009).
In conclusion, the tropical countries of Latin America, Africa, and Asia studied have some similarities in the importance of applied research subjects, and their dependence on foreign initiatives, but there are also crucial differences.Although science in Vietnam is developing and shows a positive trend in number of papers and citations, most of the impact found in this study results from minor participation of Vietnamese authors in large international projects.This important conclusion that we obtain from our data sadly matches the findings and call made over a decade ago by Hien, who stated that Vietnam depended too much on foreign authors, and called for more multidisciplinary work and internationally-recognized standards (Hien, 2010).For a more robust development of local science, the country should significantly enhance collaboration among Vietnamese institutes in order to lessen its dependence on overseas projects, even if at the beginning this causes a fall in the impact of their work as measured by this particular database.
Ethical statement: authors declare that they all agree with this publication and made significant contributions; that there is no conflict of interest of any kind; and that we followed all pertinent ethical and legal procedures and requirements.All financial sources are fully and clearly stated in the acknowledgements section.A signed document has been filed in the journal archives.

ACKNOWLEDGMENTS
We are grateful to Carolina Seas for her valuable help with the manuscript, and we thank three anonymous reviewers for careful and useful suggestions to improve the manuscript.

Fig. 2 .
Fig. 2. Number of articles and citations per publication by year.
Appendix 1 presents the 10 most productive institutions in Vietnam.The Vietnam Academy of Science and Technology ranked top in the all six publication indicators with TP of 5 673 articles (18 % of articles), IP of 835 articles (21 % of 3 898 institute independent articles), a CP of 4 838 articles (18 % of 27 318 inter-institutionally collaborative articles), a FP of 2 496 articles (8.0 % of 31 216 first-author articles), a RP of 2 343 articles (7.6 % of 30 911 corresponding-author articles), and an SP of 395 articles (20 % of 1 951 single-author articles).The Oxford University Clinical Research Unit published 782 articles, therein three single-institute articles and two single-author articles had a CPP 2018 of 58, the highest value.

Fig. 3 .
Fig. 3. Characteristics of publication type and their citations per publication.TP: total articles, NFR: both first and corresponding-authors are not from Vietnam, NR: corresponding-author is not from Vietnam, NF: first-author is not from Vietnam, IC: internationally collaborative articles, NC: nationally collaborative articles, II: institutional independent articles, CI: Vietnam independent articles, FP: first-author is from Vietnam, RP: corresponding-author is from Vietnam, FR: both first and corresponding-authors are from Vietnam.
by U.P.N.Tran, K.K.A. Le, and N.T.S. Phan from the Department of Chemical Engineering at the HCMC University of Technology.

Fig. 4 .
Fig. 4. Development of the top five Web of Science categories.

Fig. 5 .Fig. 6 .
Fig. 5. Distribution of the top 20 productive Web of Science categories in the Science Citation Index Expanded.

TABLE 1
TP: number of publications; AU: number of authors; APP: number of authors per publication; TC 2018 : the total number of citations from Web of Science Core Collection since publication to the end of 2018; CPP 2018 : number of citations (TC 2018 ) per publication (TP).
Weinstein et al. (2014)ltshuler et al. (2015)with TC 2018 of 2 385;Hammerman et al. (2012)with TC 2018 of 1 725; andWeinstein et al. (2014)with TC 2018 of 1 121.The large size of these projects is reflected in the number of authors, which range from 18 to 774.The journal with the highest IF 2018 (5.833) was the Journal of High Energy Physics with 155 articles, followed by Physical Review B (IF 2018 = 3.736) with 148 articles, and PLoS One (IF 2018 = 2.776) with 393 articles.Journals with the lower impact factors but still high in the rank included Zootaxa with an IF 2018 of 0.990, and the Journal of the Korean Physical Society with an IF 2018 of 0.63.

TABLE 2
Top 11 Web of Science categories with TP > 1 000 (Percentage from a total of 17 720 articles)

Table 6 in
Appendix 1 presents the top 10 oversea institutions that collaborated with Vietnam in research publications with three publication indicators TP, FP, and RP, and citation indicator CPP 2018 .Vietnam collaborated the most articles with University of Oxford in the UK, at 1 151 articles.The Russian Academy of Sciences had 692 collaborative articles with Vietnam including 280 first-authors articles and 286 corresponding-author articles.Collaborative articles with Heidelberg University in Germany had the highest CPP 2018 (63), followed by University of Oxford in the UK with a CPP 2018 of 52 and the University of Edinburgh, also in the UK, with a CPP 2018 of 50.

TABLE 3
Top ten most productive journals

Bibliometrics of Vietnam Publications in the Science Citation Index: general trends and comparison with other tropical countries Authors
TP: number of publications; AU: number of authors; APP: number of authors per publication; TC2018: the total number of citations from Web of Science Core Collection since publication to the end of 2018; CPP2018: number of citations (TC2018) per publication (TP).TP*: number of articles with author information; AU: number of authors; NR: number of cited reference; PG: page counts.Nguyễn Thị Nha Trang 1 , Julián Monge-Nájera 2 & Yuh-Shan Ho 3 * 1.Department of Biotechnology, College of Health Science, Asia University, No. 500 Lioufeng Road, Wufeng, Taichung 41354, Taiwan; nhatrangnguyen113@gmail.com 2. Laboratorio de Ecología Urbana, Vicerrectoría de Investigación, Universidad Estatal a Distancia, 2050 San José, Costa Rica; julianmonge@gmail.com 3. Trend Research Centre, Asia University, No. 500 Lioufeng Road, Wufeng, Taichung 41354, Taiwan; ysho@asia.edu.tw*Correspondence