We calculated the similarity of 10878 pairs of the research fields for 2010-2019 and for 2000-2009 on base of Dimensions data. The similarity of the research fields is assessed by Jaccard index. The most tied research fields for 2010-2019 are Specialist Studies in Education and Curricular and Pedagogy, whereas this pair holds rank #6 for 2000-2009. Dynamics of Jaccard index distributions does not confirm a hypothesis about increasing the share of interdisciplinary research over time. It is detected that the most collaborated research field for the both time intervals is Mechanical Engineering. This research field has maximum sum of Jaccard indexes with all the other research fields (so called stickiness index). It is detected that the most tied triad of research fields for the both time intervals are Commercial Services, Marketing, and Tourism. Distribution of similarity of the research fields, distribution of stickiness of single research field, and distribution of stickiness of triad of the research fields look like to Zipf law with 3 stable zones.
The question of how strong the various research fields are interconnected has a long
history. The relevance of the quantitative assessment of a similarity of the research
fields has intensified recently, when we are increasingly hearing about
interdisciplinary research, about PhD theses on boarding line of specialties, about multi-skill
research team etc. Traditionally, a similarity of the research fields is assessed by
experts. The assessment is based on subject matters under investigation and can be
associated with an essentialist view. In [
Recently, citations-based approach to similarity assessment of the research fields is
most widely used. This approach is based on Porter’s metrics of paper
interdisciplinary [
Due to the different content of various papers of the same journal the journal-based
classification to research field produces some errors. Moreover the journal-based
classification would not allow categorize grants, patents, books etc. It is the reason to
create in [
Dimensions uses a short version of the Australian and New Zealand Standard Research Classification. There are 154 fields of research and 22 domains. For example, domain 01 – Mathematical Sciences contains the following research fields: 0101 – Pure Mathematics; 0102 – Applied Mathematics; 0103 – Numerical and Computational Mathematics; 0104 – Statistics; 0105 – Mathematical Physics.
At the moment, Dimensions indexes 106M research papers. Each paper is assigned to one or several research fields. Most filled research field is Clinical Sciences with 9.3M papers. Distributions of papers by the research fields for 2010-2019 and for 2000-2010 are shown in Figure 1. Both distributions look pretty much as Zipf law in almost whole range.
Dimensions provides a number of papers assigned with some research field. Additionally Dimensions provides number of above mentioned papers, which assigned with each other of the research fields. It allows obtain data for calculation a similarity of any pair of research fields using just 2 queries. For processing all the research fields it is necessary one query per one research field.
We propose to assess a similarity of two research fields A and B by Jaccard index: S( A, B)
N AB N A N B N AB , where N A denotes a number of papers in research field A, N B denotes a number of papers in research field B, N AB denotes a number of papers assigned to research field A and to research field B simultaneously.
Consider the following example with the real data. There are 74519 papers assigned to Marketing in 2010 – 2019, 11843 of them also belong to Tourism. Research field Tourism has 36274 papers, hence the similarity of Marketing and Tourism equals to 11843 / (74519+36274-11843)=0.12.
Distributions of Jaccard index for two research fields are shown in Figure 2. For
reliability reason tiny research fields with less than 1000 papers for any of the decades
are out of consideration. In total 147 research fields are considered, hence the
similarity of 10878 pairs of the research fields for 2010-2019 and for 2000-2010 are
calculated. Most of the research fields have zero similarity. Both distributions look like
as three-zone Zipf law: the first zone for high similar research fields; the second zone
for low similar research fields; the third zone for tiny similar research fields. A strong
decreasing the similarity over ranks takes place for the first and the third zones.
Figure 2 shows that the leaders for 2000-2010 have higher Jaccard indexes than
leaders for 2010-2019. But, distribution for 2010-2019 has more heavy tail. It allows
to inference by eye that there is no significant difference in change of interdisciplinary
research share over time. This conclusion concordances with a result in [
The following pairs of the research fields from top-halves of the distributions in Figure 2 changed their Jaccard index drastically during the last decade: Environmental Engineering and Manufacturing Engineering – +254.5%; Atmospheric Sciences and Aerospace Engineering – -67.1%.
Twenty most tied pairs of the research fields are ranked in Figure 3 and Figure 4. Similarity of all the research fields in Figure 3 and Figure 4 are reasonable. There is one significant change over years in the tops-20 – Specialist Studies in Education with Curricular and Pedagogy moved from #6 for 2000-2009 to #1 for 2010-2019.
As an example, Figure 5 shows similarity of research fields that belong to Information and Computer Sciences domain. There are 8 research fields (A), (B), …, (H) in the domain. They are contoured by a blue rectangle in the Figure 5. Seven research fields that most tied with research fields (A), (B), …, (H) are also shown on Figure 5. Among those seven research fields Communications Technologies is most tied with Information and Computer Sciences domain.
Let’s introduce stickiness index G( A) of a research field A as a sum of all Jaccard indexes between A and other research fields as follows:
G( A)
S( A, p) , p: pF, p A where F denotes a set of the research fields. Stickiness indexes allow to detect research fields with the highest attractive to collaboration, with the highest ability to interdisciplinary. The distributions of single research field stickiness indexes are shown in Figure 6. Both distributions have very heavy tails, hence difference in 5-10 positions is not important.
Fig. 5. Similarity of research fields that belong to Information and Computer Sciences domain (data for 2010-2019)
The highest stickiness index has Mechanical Engineering for both time intervals (Figure 7 and Figure 8). Comparing the top-rank lists, it is found that Mechanical Engineering has lost their gap. Some significant differences in Figure 6 and Figure 8 are as follows: Environmental Science and Management jumped from #17 to #2, Condensed Matter Physics descended from #2 to #20+. The following research fields from the top halves of the distributions changed their stickiness indexes significantly during the last decade:
Ecological Applications – Aerospace Engineering – Atmospheric Sciences – Optical Physics – Language Studies – Astronomical and Space Sciences – Genetics – Environmental Science and Management – Condensed Matter Physics – Soil Sciences – Curriculum and Pedagogy – Civil Engineering – +46.7%; -37.7%; -28.2%; +27.6%; -27.4%; -25.9%; +25.0%; +24.6%; -24.6%; +23.9%; +22.7%; -20.5%.
A similarity of triad of research fields (A, B, C) is proposed assess by so called triad stickiness index G( A, B, C) as follows:
G(A, B, C) S(A, B) S(A, C) S(B, C)
We found 110451 triads for 2000 – 2009 and 135503 triads for 2010 – 2019 with non-zero stickiness index. Distributions of the triad stickiness indexes (Figure 9) and distributions of Jaccard indexes of pairs of research fields (Figure 2) have the same shape.
Dozens of the most tied triads are shown in Table 1 and Table 2. All the triads are reasonable. Leader for the both time intervals is Commercial Services, Marketing and Tourism. For this triad we constructed iteratively a map of science with nearest research fields (Figure 10). On each iteration we choose a research field that maximizes new net stickiness index. The iteration traces are present at right part of Figure 10. It starts with Business and management, and finishes on Historical Studies. Figure 10 shows that research fields with the same domains are stronger tied each other than with research fields from different domains. It may considerate as an indirect support for proposed stickiness index.
Film, Television and Digital Media Journalism and Professional Writing Communication and Media Studies Urban and Regional Planning Transportation and Freight Services Human Geography Education Systems Curriculum and Pedagogy Specialist Studies In Education Curriculum and Pedagogy Specialist Studies In Education Linguistics Curriculum and Pedagogy Specialist Studies In Education Sociology Ecological Applications Environmental Science and Management Ecology Geochemistry Geology Geophysics Design Practice and Management Art Theory and Criticism Visual Arts and Crafts Civil Engineering Urban and Regional Planning Transportation and Freight Services Art Theory and Criticism Performing Arts and Creative Writing Visual Arts and Crafts Curriculum and Pedagogy Specialist Studies In Education Psychology Stickiness index 0.4669
Urban and Regional Planning Transportation and Freight Services Human Geography Film, Television and Digital Media Journalism and Professional Writing Communication and Media Studies Civil Engineering Urban and Regional Planning Transportation and Freight Services Language Studies Linguistics Literary Studies Geochemistry Geology Geophysics Design Practice and Management Art Theory and Criticism Visual Arts and Craft Building Commercial Services Tourism Geochemistry Geology Physical Geography and Environmental Geoscience Architecture Urban and Regional Planning Transportation and Freight Services Art Theory and Criticism Visual Arts and Crafts Curatorial and Related Studies Environmental Science and Management Urban and Regional Planning Transportation and Freight Services Stickiness index 0.5307
For the first time similarity of the research fields in form of Jaccard index are assessed by Dimensions data. Source information for Jaccard index calculation is the statistics of categorized papers in Dimensions. It is calculated the similarity of 10878 pairs of the research fields for 2010-2019 and for 2000-2009. The most tied pair of the research fields for 2010-2019 is Specialist Studies in Education and Curricular and Pedagogy, whereas they hold rank #6 for 2000-2009. The following pairs of the research fields changed their Jaccard index drastically during the last decade: Environmental Engineering and Manufacturing Engineering jumped on 254.5%, Atmospheric Sciences and Aerospace Engineering dropped on 67.1%.
Stickiness index of a research field is introduced as an assessment of its attractiveness to be a member in an interdisciplinarity group. Stickiness index is a sum of all Jaccard indexes related to current research field. The highest stickiness index has Mechanical Engineering for both time intervals. The following research fields changed their stickiness indexes drastically during the last decade: Ecological Applications jumped on 47%, Aerospace Engineering dropped on 38%.
The most tied triads of research fields are detected on base of the proposed stickiness index. All the triads are reasonable. Leader among the triads is Commercial Services, Marketing and Tourism for the both time intervals.
Possible applications of proposals similarity index is categorization of researchers, universities, journals, which act in various research topics. Similarity index allows taking into account tails in the research profile for more correct categorization.