2. Materials and methodology
2.1 Data collection
Web of Science is an internationally recognized database that reflects the level of scientific research in a field. Among the resources included in Web of Science are the Science Citation Index Expanded (SCI-E), Social Science Citation Index (SSCI) and other citation index databases, such as Journal Citation Reports (JCR) and Essential Science Indicators (ESI), which are well known in the global technology and education fields. In this study, we used the SCI-E and SSCI databases from the Web of Science core collection (WoSCC) as the object database and set TI=((“Seed dispersal” OR “Wind dispersal” OR “Dispersal by birds and mammals” OR “Myrmecochory*” OR “Water and ballistic dispersal” OR “Evolution of dispersal” OR “Secondary dispersal” OR “Indirect seed dispersal” OR “Two-phase dispersal” OR “Two-stage dispersal” OR “Multi-phase dispersal”) OR (“Seed dispersal” AND Diploendozoochory*)) as the retrieval condition, with a time span of 1985-2020, to search for related results about seed dispersal. The WoSCC is one of the main databases for bibliometric analysis (Mongeon and Paul-Hus 2016). The retrieved records were downloaded and saved as a plain text file in the ”Full Record and Cited References” format and used as a sample of the data analysed in this study.
2.2 Methodology
2.2.1 Bibliometric analysis methods
Bibliometrics is a form of mathematical statistics used to analyse academic literature quantitatively (Nakagawa 2004). CiteSpace software is currently one of the analysis tools applied most often in the field of bibliometric analysis (Huang 2019). It is an application program for literature analysis and visualization and was developed by Dr Chen (Chen 2006). The 5.7 R2 version of CiteSpace for 64-bit Windows with Java 8 was used. In this study, we focused on the assessment of three quantitative characteristics of the bibliometric data with (1) co-occurrence analysis, (2) collaboration networks, and (3) co-citation analysis. Details of the analysis process in this study are shown in Fig. 1.
2.2.2 Activity index (AI) and attractive index (AAI)
On the basis of existing research (Schubert and Braun 1986, Chen and Guan 2011, Shen et al. 2018), we employed two indicators in this study, the activity index (AI) and the attractive index (AAI), to assess changes in the research effort and academic impact of different countries in the field of seed dispersal over time.
The AI can measure the degree of relative effort of a country in a research field; it can be calculated with the following formula:
\(\text{AI}_{i}^{t}=\frac{P_{i}^{t}/\sum P}{\text{TP}^{t}/\sum\text{TP}}\)(1)
The AAI can evaluate the impact of a country on a research field through the number of citations of publications. This index can be calculated with the following formula:
\(\text{AAI}_{i}^{t}=\frac{C_{i}^{t}/\sum C}{\text{TC}^{t}/\sum\text{TC}}\)(2)
In the formulas, \(\text{AI}_{i}^{t}\) and \(\text{AAI}_{i}^{t}\)represent the AI and the AAI of country i in year t, respectively;\(P_{i}^{t}\) and \(C_{i}^{t}\) represent the number of articles and citations of publications on seed dispersal from country i in year t; and \(\sum P\) and \(\sum C\) represent the total number of articles and the sum of citations to publications related to seed dispersal from country i during a period of time. Furthermore,\(\text{TP}^{t}\) and \(\text{TC}^{t}\) represent the global number of articles and citations of publications in year t;\(\sum\text{TP}\) and \(\sum\text{TC}\) represent the total number of articles and the sum of citations globally during the same period as that of \(\sum P\) and \(\sum C\), respectively.
In these formulas, when \(\text{AI}_{i}^{t}=1\) and\(\text{AAI}_{i}^{t}=1\), the research effort and academic impact, respectively, of country i in year t are equal to the global average. In addition, when \(\text{AI}_{i}^{t}>1\) or \(\text{AI}_{i}^{t}<1\), the research effort of country i in year t is higher or lower than the global average, and when \(\text{AAI}_{i}^{t}>1\) or\(\text{AAI}_{i}^{t}<1\), the number of citations of publications from country i in year t is more or less, respectively, than the global average level of citations.