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.