“…However, such activities are not formally documented and cannot be easily ascertained. There are also other ways of tracking scholarly communication and collaboration, such as the study of acknowledgments (Cronin & Overfelt, 1994;Laudel, 2002), citations (Bornmann, Mutz, Neuhaus, & Daniel, 2008;Garfield, 1972;Rahm & Thor, 2005;Sims & McGhee, 2003;Smith, 1981), and co-citations (Acedo & Casillas, 2005;Gm€ ur, 2003;He & Hui, 2002;Small, 1999) in publications. Such collaboration is known as "invisible" (Laudel, 2002), whereas coauthorship is the most tangible, widely used, and best-documented form of collaboration (Gl€ anzel & Schubert, 2005;Smith, 1958).…”