How US publishing market is changing in unit by formats

According to the report from The Association of American Publishers, the publishing market has met the great change in the U.S. in last 3 years.

The report includes sales revenues, market shares, and net unit sales by publishing formats such as hardcovers, softcovers, paperbacks, and e-books and non-physical formats.  It is not surprising so much that the e-books is growing so fast and largely, but the hardcover books are still growing slightly.