Proposal and application of the interdisciplinarity borrowing index: Determining the degrees of interdisciplinarity of ILS dissertations



This work proposes an interdisciplinary borrowing index and applies this index to the field of Information and Library Science. The study examines the interdisciplinarity of LIS dissertations, with an emphasis on evolution of the disciplinary influences on the field over time.


One element of diversity in scholarly communication is the degree to which scholars engage in interdisciplinarity. Interdisciplinarity is continuing to increase across many areas of research (Morillo, Bordons, & Gómez, 2003) and is heavily promoted by funding agencies and academic institutions (Bordons et al., 1999; Haythornthwaite, 2006; Porter et al., 2007). Interdisciplinary research is defined by Porter et al. (2007) as being a mode of research by teams of individuals that integrate 1) perspectives/concepts/theories, 2) tools/techniques, and/or 3) information/data from two or more bodies of specialized knowledge or research practice. Porter et al. (2007) differentiate interdisciplinarity, multidisciplinarity and transdisciplinarity as separate concepts, while other researchers consider interdisciplinarity the umbrella term under which the rest of the terms fall (Morillo, Bordons, & Gómez, 2003). For the sake of simplicity, interdisciplinarity in this context will be defined as the “integration of disciplines within a research environment” (Qin, Lancaster, & Allen, 1997).

Collaboration is a common and important feature of interdisciplinary work and has been studied by researchers such as Palmer (1999), Qin, Lancaster, & Allen (1997) and Bordons et al. (1999). Pierce (1999) identified two other types of interdisciplinary information transfer in addition to collaboration. Pierce defined collaboration as researchers from different disciplines working together on a single publication. To collaboration Pierce (1999) added borrowing: importing theories or methods from other disciplines into the literature of your own discipline (typically done through the use of citations) and boundary crossing: the publishing of work in a discipline different from the disciplinary affiliation of the author, thereby exporting theories and methodology from one discipline to another.

Porter et al. (2007) proposed measurements of interdisciplinarity that evaluated the integration and specialization of researchers/disciplines. This measurement relies on the extent to which the researcher cites outside of their discipline and the diversity in publication outlets of the given researcher. In order to calculate the proposed interdisciplinary score, Porter et al. (2007) created a co-citation matrix of all the intercitations between Web of Knowledge journal subject categories. The authors use the values of this cosine matrix to determine scores on three measures of interdisciplinarity: specialization, integration, and reach. The foundation of their metric is not only on the degree to which an author cites and is cited by disciplines outside of their own, but the degree of relatedness among those disciplines. Other research has also utilized Web of Science and bibliometric techniques (Ding, Foo, & Chowdhury, 1998) and a few researchers have combined quantitative bibliometric measures with social network analysis techniques and various qualitative metrics (such as loosely structured interviews) (White, Wellman, & Nazer, 2004; Palmer, 1999; Qin, Lancaster, & Allen, 1997) in order to understand interdisciplinarity.

Research Questions

Building on the previous research, we examine ways in which interdisciplinarity can be measured for multiple source types and without the construction of a full “map of science” co-citation matrix. The goal of this is to provide a simple index for interdisciplinarity, which can be used to compare similar units of analysis. Once constructed, the application of this will be used to examine the extent to which ILS borrows from other disciplines. Our research questions for the project are specified below:

  • 1To what extent can degrees of interdisciplinary borrowing be represented in a simple index?
  • 2How interdisciplinary are ILS dissertations? How has the degree of interdisciplinarity changed over time?
  • 3What are the primary disciplines influencing ILS dissertations (as shown through citations)? How has that changed over time?

Interdisciplinarity Borrowing Index

The interdisciplinary borrowing index proposed is informed by Pierce's (1999) operationalization of the concept of interdisciplinarity. Using Pierce's element of borrowing, this index quantifies the degree of borrowing as an index of interdisciplinarity. To assess this, the following formula is suggested:

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where d=number of unique disciplines in addition to the core discipline, i=the number of references classified within the core discipline and n=the total number of references (the constant will be explained in the pilot study section). For example, in the case of an ILS dissertation containing 200 references, 130 of which were classified as ILS, i would equal 130 and n would equal 200. If the remaining 70 references were split across three different disciplines (e.g., education, psychology, and history) d would equal 3. The end equation would therefore be:

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As an indicator of degree of interdisciplinarity, a higher number would represent a higher degree of interdisciplinarity. For example, considering the example above, if the 70 remaining references had actually been classified into 7 different disciplines, the equation would have looked like this:

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The second figure represents a reference list with a higher degree of interdisciplinarity because it contains more representative disciplines. While the number of additional disciplines is therefore heavily weighted in this index, the percentage of within-field references also moderates the index. For example, in the figure above, if the denominator were 1.05, indicating that 95% of the references were from the core discipline, the total interdisciplinarity index would decrease, indicating a lower degree of interdisciplinarity. The interdisciplinary borrowing index could be generated for any unit — a single type of source in a reference list, the entire reference list of a single work, all the references from a journal, all the references in a scholar's oeuvre, etc.

Pilot Study

In order to test and refine the methods, a pilot study was conducted on 15 dissertations from a single institution. These dissertations represented a range of topic areas and were conducted under multiple advisors. The dissertations were completed between 1999 and 2007. The following steps were conducted in order to compile interdisciplinary borrowing index for these dissertations:

  • 1A database was compiled that listed the ID for each dissertation, the year the dissertation was completed, a type code (journal, conference proceeding, book, etc.) and a source title for each reference in the dissertation bibliography.
  • 2For journals and conference proceedings, a search was conducted using Urlich's Serials Directory, Web of Science, and the ACM Digital Library in order to find the most current title for each source. (For example, this would identify American Documentation as a previous title and the Journal of American Society for Information Science and Technology as a current title.) This allows for all previous titles to be aggregated under one source title name.
  • 3All types were evaluated to their overall contribution and to the individual type composition for each dissertation.
  • 4Source title overlaps (those titles utilized in more than one dissertation) were identified as potential “core” literature.
  • 5Journal titles were classified by discipline using Web of Knowledge. Specifically, the journal titles were searched in Web of Science and the top “subject area(s)” for the result set was used as an indicator of discipline.
  • 6Book titles were classified by discipline using WorldCat. Specifically, the book titles were searched in WorldCat and the entry utilized by the most libraries was used to locate the LC class. The general class was used to identify discipline (for example, BF = psychology).
  • 7The interdisciplinary borrowing index was then generated for those references coded as journals or books.

The pilot study provided valuable refinements and insights into the proposed methods. For instance, in the first ILS dissertation coded, there was not a single journal or conference paper that fell into the ILS subject category. Therefore, a constant was added to the denominator to eliminate the possibility of the denominator equaling zero. In addition, the results from the pilot showed that journals were the most frequently cited sources (41% of the 2349 references coded), followed by books (30%) and conference proceedings (17%). The remaining categories (including categories for technical reports, dissertations/theses, personal communications, unpublished manuscripts, etc.) each contributed less than 3% to the overall number of references. Of all categories, there was the greatest degree of overlap in the journal and conference proceeding source titles. There was very little overlap in terms of books — many of those which overlapped were research methods textbooks.

Future Work

Moving forward from the lessons learned from the pilot, the next stage of research will evaluate a set of 100 dissertations from current ILS faculty members who received their degrees within the field of ILS. These dissertations will be gathered from multiple decades in an attempt to show the change in interdisciplinarity over time. The interdisciplinary borrowing index will be applied to all of these. In addition, indications of the core sources of the field will be gathered by analyzing those sources which occur most frequently among the dissertations.

This work will provide a measurement of the degree of interdisciplinarity within our field and the disciplines which have had and are having the largest impact on our field.