Total sales in the U.S. book publishing industry rose 4.6% in 2014 over 2013, according to figures released Wednesday morning by the Association of American Publishers.

The biggest increase came in the K-12 instructional materials segment, where sales rose 9.9%. Sales in the professional segment increased 4.6%, while sales in the trade category rose 4.2%. The trade remained the largest category, with 2014 revenue of $15.43 billion.

Total units increased 3.7%, hitting 2.70 billion; units in the trade category rose 4.1%, to 2.42 billion. The AAP includes religion publishing in the trade category, along with adult and children’s sales. The estimate for the entire industry is based on actual sales supplied by about 1,800 U.S. publishers for both 2013 and 2014, which the AAP then augments by using a variety of sources to estimate sales for publishers that do not report data. The AAP took over the creation of annual sales statistics this year after its agreement with BISG to develop industry data through BookStats was not renewed.

As the AAP’s earlier data had shown, the fastest-growing category in the trade segment was children’s/young adult where sales rose 20.9%, to $4.40 billion, and units increased 13.5%. Sales of adult fiction fell 2.0% in the year and nonfiction dropped 1.1%.

After slightly declining last year, total e-book sales increased 3.8% to an estimated $3.37 billion dollars, the StatShot Annual showed, although units rose only 0.2%. E-book sales do not include sales of the format through subscription services and the AAP estimated that sales of e-books through the subscription channel were over $20 million based on reports from about 20 publishers. Downloadable audio sales grew 26.8% in the year and sales of subscription audio rose 26.8%. The AAP estimated that 3.88 million audiobooks were sold through subscription services, while 2.47 million e-books were sold through the channel.

“The industry’s health is driven by the depth and range of titles and formats produced by publishers. By that measure, 2014 was a good year for publishers with more than 2.7 billion books in all formats sold and continuous innovation in developing new ways for readers to enjoy and learn from books,” said Tina Jordan, AAP v-p.