The Hot and Cold Book Categories of 2015 has some really juicy stuff. Those adult coloring books...Who would have thought?
The article says that "The classics segment got a nice bump from the publication of Harper Lee's Go Set a Watchman, which caused a surge in sales of To Kill a Mockingbird." So I'm assuming these sales figures are not for books published just in 2015 but for back list books, too. This article also doesn't say if these numbers include self-published titles. I'm going to guess they don't, or they would have been much higher.
Okay, so now what I'm wondering about is the number of new titles published each year and how that compares with the units sold. The best number I can find for new traditional titles is for 2013, and it's around 305,000. That's the number of titles, not the number of copies of each title. What I'm trying to wrap my head around is how many individual books are out there and how many of them find a home.