The lists are divided among fiction and non-fiction, print and e-book, paperback and hardcover; each list contains 15 to 20 titles. The lists have been subdivided several times. "Advice, How-To, and Miscellaneous" debuted as a list of five on January 1, 1984. It was created because advice best-sellers were sometimes crowding the general non-fiction list. Its inaugural number one bestseller, "The Body Principal" by Victoria Principal, had been number 10 and number 12 on the non-fiction lists for the two preceding weeks. In July 2000, the "Children's Best Sellers" was created after the Harry Potter series had stayed in the top spots on the fiction list for an extended period of time. The children's list was printed monthly until February 13, 2011, when it was changed to once an issue (weekly). In September 2007, the paperback fiction list was divided into "trade" and "mass-market" sections, in order to give more visibility to the trade paperbacks that were more often reviewed by the newspaper itself. In November 2010, "The New York Times" announced it would be tracking e-book best-seller lists in fiction and nonfiction starting in early 2011. "RoyaltyShare, a San Diego-based company that tracks data and aggregates sales information for publishers, will ... provide [e-book] data". The two new e-book lists were first published with the February 13, 2011, issue, the first tracks combined print and e-book sales, the second tracks e-book sales only (both lists are further sub-divided into Fiction and Non-fiction). In addition a third new list was published on the web only, which tracks combined print sales (hardcover and paperback) in fiction and nonfiction. In December 16, 2012, the children's chapter books list was divided into two new lists: middle-grade (ages 8–12) and young adult (age 12–18), both which include sales across all platforms (hard, paper and e-book).