... It is widely recognized that a critical mass (Rohlfs, 1974Rohlfs, , 2001 Reinganum, 1981; Cabral, 1990; Shapiro and Varian, 1999) of users or complementary products must be established in order for growth to continue in industries that display strong initial direct or indirect network effects (Katz and Shapiro, 1985; Arthur, 1994; Katz and Shapiro, 1994; Ryan and Tucker, 2006). In industries that display strong initial direct network effects, a critical mass of users is needed for users to receive sufficient value from the use of products such as the telephone, fax machine, or social networking services (Rohlfs, 1974Rohlfs, , 2001 Shapiro and Varian, 1999). In industries that display strong indirect network effects, a critical mass of complementary products (e.g., hardware and software) are needed for users to receive sufficient value from the use of computers, video games, or video or music players (Grindley, 1995; Gandal et al, 2000; Dranove and Gandal, 2003; Ohashi, 2003; Nair et al, 2004; Clements and Ohashi, 2005). ...