**2. Literature review**

The French school of proximity dynamics was pioneer to consider other notions of proximities beyond the geographical [12–14]. Drawing upon this line of research, Boschma [15], from a theoretical point of view, identified five kinds of proximities: geographical, cognitive, institutional, social, and organizational. Recent research has also highlighted the relevance of economic differences as an explanatory factor of SC [5, 10, 11, 16]:

• *Geographical distance* among actors hinders SC because face-to-face interactions that facilitate knowledge flows and tacit knowledge sharing become costly as distance increase

<sup>1</sup> Note that we do not perform a detailed analysis for *medicine & biomedicine* because some of the publications may be associated with university hospitals, which may have been or not co-authored by academics. Publications, for which we could not establish a clear link with an academic institution, have been excluded from our sample. Thus, our study may underestimate the scientific output in this discipline.

(e.g. [4, 17, 18]). Despite some authors claimed the death of distance due to ICT development, Hoekman et al. [18] found that physical distance still impedes research collaboration, with no evidence of a declining effect in the period 2000–2007.

single-authored papers; learning, social networks creation, knowledge diffusion, and crossfertilization across individuals and/or disciplines are enhanced. From an economic viewpoint, SC also provides benefits including access to a wide variety of resources and new foundations or instruments. These benefits, together with the well-known role of knowledge creation and diffusion as the main sources for sustainable economic growth in the long run [6, 7], have shaped the European policy. The European government initiative aimed to convert Europe into the "the most competitive and dynamic knowledge-based economy" [8] giving priority to invest more in knowledge and innovation and to give Europe a new "fifth liberty," the free

The contribution of this research is twofold. First, we provide a comprehensive analysis of the evolution of geographical, cognitive, institutional, social, and organizational proximity on scientific collaboration. Apart from these, we also add economic distance as suggested in the recent literature [10, 11]. Second, we provide a joint analysis of trends in SC in all disciplines included in the Science Citation Index (SCI) of the Web of Science (WoS), and a separated analysis for *Chemistry & Chemical*, *Life Sciences* and *Physics and Astronomy* in order to examine whether there are differences across disciplines. We have chosen these disciplines because, jointly with *Medicine & Biomedicine*, they have the highest publication and collaboration share1

For our purpose, we use an original dataset containing information on 152,140 collaborations in publications in Science and Engineering (excluding social sciences) indexed in the Science Citation Index (SCI) provided by WoS and co-authored among academics from different universities. Our analysis includes 175 public universities from peripheral countries in Southern Europe: Spain, Greece, Italy, and Portugal. Focusing on peripheral countries is relevant because they usually include universities and regions far from core centers of knowledge with the lower level of resources and fewer opportunities to integrate in collaboration networks.

The remainder of the chapter is organized as follows. In Section 2, we review the relevant literature. Section 3 describes the data and explains the methodology. Section 4 provides the results. The main conclusions and policy implications are obtained at the end of the paper.

The French school of proximity dynamics was pioneer to consider other notions of proximities beyond the geographical [12–14]. Drawing upon this line of research, Boschma [15], from a theoretical point of view, identified five kinds of proximities: geographical, cognitive, institutional, social, and organizational. Recent research has also highlighted the relevance of

• *Geographical distance* among actors hinders SC because face-to-face interactions that facilitate knowledge flows and tacit knowledge sharing become costly as distance increase

Note that we do not perform a detailed analysis for *medicine & biomedicine* because some of the publications may be associated with university hospitals, which may have been or not co-authored by academics. Publications, for which we could not establish a clear link with an academic institution, have been excluded from our sample. Thus, our study may

economic differences as an explanatory factor of SC [5, 10, 11, 16]:

**2. Literature review**

30 Scientometrics

underestimate the scientific output in this discipline.

1

.

circulation of knowledge in order to construct a European research area [9].

