Ten years ago, I studied readers of the then popular Left Behind series of Christian apocalyptic novels. If I conducted that study today, I would potentially have access to far more objective data about readers than I did. How quickly do they read? Where do they stop reading? What passages do they mark? Do they write notes in the margins?
E-books are providing companies with the opportunity for all of this information and more about people who use e-readers like the Nook and Kindle.
Journalists covering religion regularly cite membership figures for the various religious organizations. They want to give readers an idea of how many people might be affected by developments in a particular group or tradition.