“…In our study, clear market definitions are important because firms defined to be a pharmaceutical firm's rivals should be actual, meaningful competitors whose products are substitutes for those of the pharmaceutical firm. Defining markets by therapeutic classes is widely-accepted and commonly-used by U.S. government authorities, industry players, and academic researchers (Anand, Mesquita, & Vassolo, 2009;Lerner, 1997;Rothaermel, 2001;Vassolo, Anand, & Folta, 2004).…”