Polygraph have used Spotify to measure the popularity of older music, specifically tracks from the 90's. By analysing the data interesting trends are visable, popularity at the time doesn't always translate into longevity. For example the top track is Nirvana's 'Smells like teen spirit' which didn't get into the top 5 when first released. It's worth noting that Spotify doesnt have every artist, and the user base of the app skews young. Check out the Polygraph website for more Spotify data mining.