Economists Luis Aguiar and Joel Waldfogel looked at music sales in countries Spotify operated in between 2013 and 2015, and concluded that yes, “Spotify use displaces permanent downloads” — that is, if you’re getting your music from Spotify, you don’t need to buy it from iTunes. But they also found that “Spotify displaces music piracy,” and that the two trends balance each other out: “Interactive streaming appears to be revenue-neutral for the recorded music industry.”
Source: Spotify Shrinks Music Download Sales, Fights Piracy – Study | Re/code