In practice, it is often surprisingly difficult to predict whether new products and
technologies are complements or substitutes. As a result, we can often not be sure how
changes in copyright will influence demand and industry profitability. The entertainment
industry’s history provides many examples of the difficulties involved in distinguishing
substitutes, unrelated products, and complements. Music companies fought the
introduction of radio in the 1920s, fearing the new medium would provide close
substitutes to buying records. Since that time, the numerous attempts to bribe radio
stations in the hopes of influencing playlists suggest the industry has come to see radio as
an important complement to recordings (Coase, 1979).
Harvard-Studie (pdf) von Felix Oberholzer-Gee & Koleman Strumpf, Harvard Business School; via @library_pirate