Betweenness and diversity in journal citation networks as measures of interdisciplinarity—A tribute to Eugene Garfield

Abstract

Journals were central to Eugene Garfield's research interests. Among other things, journals are considered as units of analysis for bibliographic databases such as the Web of Science and Scopus. In addition to providing a basis for disciplinary classifications of journals, journal citation patterns span networks across boundaries to variable extents. Using betweenness centrality (BC) and diversity, we elaborate on the question of how to distinguish and rank journals in terms of interdisciplinarity. Interdisciplinarity, however, is difficult to operationalize in the absence of an operational definition of disciplines; the diversity of a unit of analysis is sample-dependent. BC can be considered as a measure of multi-disciplinarity. Diversity of co-citation in a citing document has been considered as an indicator of knowledge integration, but an author can also generate trans-disciplinary-that is, non-disciplined-variation by citing sources from other disciplines. Diversity in the bibliographic coupling among citing documents can analogously be considered as diffusion or differentiation of knowledge across disciplines. Because the citation networks in the cited direction reflect both structure and variation, diversity in this direction is perhaps the best available measure of interdisciplinarity at the journal level. Furthermore, diversity is based on a summation and can therefore be decomposed; differences among (sub)sets can be tested for statistical significance. In the appendix, a general-purpose routine for measuring diversity in networks is provided.

Interdisciplinarity as diversity in citation patterns among journals: Rao-Stirling diversity, relative variety, and the Gini coefficient

“…From the perspective of network analysis, we have explored Betweenness Centrality (BC) as an indicator of diversity and interdisciplinarity (Leydesdorff, Goldstone, & Schank, 2008). Using the aggregated journal-journal citation relations provided by the Journal Citation Reports 2015 as a comprehensive set (n > 11,000 journals), Leydesdorff, Wagner, & Bornmann (2018) tested RS Diversity and BC against each other as measures of interdisciplinarity. However, the results were disappointing: whereas BC was found to indicate "multidisciplinarity" more than "interdisciplinarity," the authors cautioned (at p. 588) that "[…] Rao-Stirling 'diversity' is often used as an indicator of interdisciplinarity; but it remains only an indicator of diversity."…”

“…However, these components can be measured independently and thereafter combined (ex post). We argue that the ex ante definition of "dual-interdisciplinarity (Leydesdorff, Wagner, & Bornmann, 2018). However, the measure can be applied to any data matrix (e.g., Bache et al, 2013).…”

Nature’s reach: narrow work has broad impact

“…Interdisciplinarity refers to integration: we define it as the diversity in inspiration in an article's references, and the diversity in how an article's impact diffuses across disciplines. Although it is difficult to assess integration across an article's citations, this measure can capture how the knowledge communicated by the article had diverse impact 6 . This analysis indicates the extent of interactions across disciplines, but does not reveal the specific details of how those disciplines interact.…”

Node2vec Representation for Clustering Journals and as A Possible Measure of Diversity

“…Following the earlier settings (Leydesdorff et al, 2018), we calculate the citingside and cited-side Rao-Stirling diversity of all journals in our set, as shown in Fig. 4.…”

“…This similarity can be defined based on co-cited or co-citing papers/journals. For example (Leydesdorff et al, 2018), for journal i and journal j, their similarity can be calculated based on their vectors of direct citations 1 2 , , ,…”