The Association of American Publishers has released "U.S. Publishing Industry's Annual Survey Reveals Nearly $28 Billion in Revenue in 2015."
Here's an excerpt:
Revenues and unit volume were essentially flat with a decrease of 0.6% from $27.96 billion in revenue from 2014, and a 0.5% increase in units from 2.70 billion units in 2014 (chart below). . . .
eBooks: After peaking in 2013 at $3.24 billion, eBook revenue declined to $3.20 billion in 2014 and again in 2015 by 11.3% to $2.84 billion. Unit sales also declined by 9.7%, with eBooks now making up 17.3% of the trade book market. . . .
Publishers saw increased revenue from trade book sales at physical retail stores for the second year in a row. In 2015, physical store sales grew 1.8% from $4.08 billion to $4.15 billion.