Bridging centrality as an indicator to measure the 'bridging role' of actors in networks: An application to the European Nanotechnology co-publication network

In the recent past, we can observe growing interest in STI studies in the notion of positioning indicators, shifting emphasis to actors in the innovation process and their R&D inter-linkages with other actors. In relation to this, we suggest a new approach for assessing the positioning of actors relying on the notion of bridging centrality (BC). Based on the concept of bridging paths, i.e. a set of two links connecting three actors across three different aggregate nodes (e.g. organisations, or regions), we argue that triangulation in networks is a key issue for knowledge recombinations and the extension of an actor's knowledge base. As bridges are most often not empirically observable at the individual level of research teams, we propose an approximated BC measure that provides a flexible framework for dealing with the aggregation problem in positioning actors. Hereby, BC is viewed as a function of an aggregate node's (i) participation intensity in the network, (ii) its openness to other nodes (i.e. the relative outward orientation of network links), and iii) the diversification of links to other nodes. In addition, we propose a generalised version of the BC measure that accounts for different node categories. An illustrative example on the European Nanotechnology co-publication network observed at the level of organisations demonstrates the usefulness and complementary interpretation power in comparison to conventional centrality measures.