A common question for new Shelfie users is “what percentage of ebooks on Shelfie are free?” This is different from what percentage of books on my shelf are eligible for a bundle deal… that’s a question I looked at in a previous post. In theory this is a really easy question to answer, a little bit of SQL and you’re done:
(SELECT count(*) FROM books WHERE price=0) / (SELECT count(*) FROM books)
The problem with the simple answer above is that it doesn’t take into account the fact that some books are more popular than others. After spending more time than I want to admit playing around with LEFT OUTER JOINs in SQL, I had a way to normalize for the popularity of titles even if we hadn’t (yet) identified that book in hundreds of thousands of pictures of Shelves that Shelfie users have submitted.
When I was thinking about this question, I thought it might be fun to expand the question and look at the full gamut of bundle prices that publishers have set for their ebooks through Shelfie. The graph below shows this distribution.
There are a few of interesting features in the data. The first is that over 30% of the bundled ebooks offered by publishers through Shelfie are free, and nearly 50% are priced at or below $0.99. As the price rises there are then a few interesting bumps in the distribution first at $2.99, again at $4.99, and finally at $9.99. Here’s what’s happening at each of those spikes:
The spike at $2.99 is the result of Macmillan’s imprint Tor — all Tor ebooks are available through Shelfie as bundled ebooks for $2.99. The bump at $4.99 is the result of the many technical publishers we have on board (e.g. O’Reilly, Wiley, and Packt) — each of these publishers have priced the bundled digital edition of their technical books at $4.99. The final spike at $9.99 is the result of several large textbook publishers who offer the bundled digital edition at $9.99 to students who purchase the print edition (which is often priced above $200, so $9.99 is a great deal for the addition of a digital copy that won’t weight down your backpack between classes).