In the last two decades there have been studies claiming that science is becoming ever more interdisciplinary. However, the
evidence has been anecdotal or partial. Here we investigate how the degree of interdisciplinarity has changed between 1975
and 2005 over six research domains. To do so, we compute well-established bibliometric indicators alongside a new index of
interdisciplinarity (Integration score, aka Rao-Stirling diversity) and a science mapping visualization method. The results
attest to notable changes in research practices over this 30 year period, namely major increases in number of cited disciplines
and references per article (both show about 50% growth), and co-authors per article (about 75% growth). However, the new index
of interdisciplinarity only shows a modest increase (mostly around 5% growth). Science maps hint that this is because the
distribution of citations of an article remains mainly within neighboring disciplinary areas. These findings suggest that
science is indeed becoming more interdisciplinary, but in small steps — drawing mainly from neighboring fields and only modestly
increasing the connections to distant cognitive areas. The combination of metrics and overlay science maps provides general
benchmarks for future studies of interdisciplinary research characteristics.
The multidimensional character and inherent conflict with categorisation of interdisciplinarity makes its mapping and evaluation
a challenging task. We propose a conceptual framework that aims to capture interdisciplinarity in the wider sense of knowledge
integration, by exploring the concepts of diversity and coherence. Disciplinary diversity indicators are developed to describe
the heterogeneity of a bibliometric set viewed from predefined categories, i.e. using a top-down approach that locates the
set on the global map of science. Network coherence indicators are constructed to measure the intensity of similarity relations
within a bibliometric set, i.e. using a bottom-up approach, which reveals the structural consistency of the publications network.
We carry out case studies on individual articles in bionanoscience to illustrate how these two perspectives identify different
aspects of interdisciplinarity: disciplinary diversity indicates the large-scale breadth of the knowledge base of a publication;
network coherence reflects the novelty of its knowledge integration. We suggest that the combination of these two approaches
may be useful for comparative studies of emergent scientific and technological fields, where new and controversial categorisations
are accompanied by equally contested claims of novelty and interdisciplinarity.
Nanotechnology has been presented in the policy discourse as an intrinsically interdisciplinary field, requiring collaborations
among researchers with different backgrounds, and specific funding schemes supporting knowledge-integration activities. Early
bibliometric studies supported this interdisciplinary vision (Meyer & Persson, 1998), but recent results suggest that nanotechnology is (yet) a mixed bag with various mono-disciplinary subfields (Schummer, 2004). We have reexamined the issue at the research project level, carrying out five case studies in molecular motors, a
specialty of bionanotechnology. Relying both in data from interviews and bibliometric indicators, we have developed a multidimensional
analysis (Sanz-Menndez et al., 2001) in order to explore the extent and types of cross-disciplinary practices in each project. We have found that
there is a consistent high degree of cross-disciplinarity in the cognitive practices of research (i.e., use of references
and instrumentalities) but a more erratic and narrower degree in the social dimensions (i.e., affiliation and researchers’
background). This suggests that cross-disciplinarity is an eminently epistemic characteristic and that bibliometric indicators
based on citations and references capture more accurately the generation of cross-disciplinary knowledge than approaches tracking
co-authors’ disciplinary affiliations. In the light of these findings we raise the question whether policies focusing on formal
collaborations between laboratories are the most appropriate to facilitate cross-disciplinary knowledge acquisition and generation.