“…Different indicators have been introduced to quantify collaboration in research papers (see for example, Egghe, 1991;Glänzel & Schubert, 2004;Vinkler, 2010) and extensive literature has been devoted to explore collaboration patterns (Bordons & Gómez, 2000) and the influence of collaboration on the productivity of scientists and on the impact of research (Abramo, D'Angelo, & Di Costa, 2009;Bordons, Aparicio, & Costas, 2013;Glänzel, 2001;Lee & Bozeman, 2005). In most recent years, the application of social network analysis to study co-authorship relations has emerged as an interesting approach, since it allows us to visualise and investigate social structures and relations (see for example, Abbasi, Altmann, & Hossain, 2011;Abbasi, Chung, & Hossain, 2012;Jansen, von Görtz, & Heidler, 2010;Li-Chun, Kretschmer, Hanneman, & Ze-Yuan, 2006;Newman, 2001;Otte & Rousseau, 2002).…”