Units fell to 204 million from 234 million in 2014. The high point of e-book sales was 2013 when units totaled 242 million units. While e-book sales fell in the year, print units rose 2.8%, to 653 million. As a result, e-books’s market share of units dipped to 24% in 2015, down from 27% in 2014. Mooney observed that some of the gain in print sales was due to the extraordinary popularity of adult coloring books last year. The e-book sales figures came from about 400 traditional publishers, Mooney said.
Source: BEA 2016: E-book Sales Fell 13% in 2015, Nielsen Reports