From the press release:
USA TODAY's Best-Selling Books List now includes sales figures from the Barnes & Noble nook and Sony's Reader™ Store in overall sales rankings. This is in addition to Kindle sales which were added in July 2009. USA TODAY is the first major book list to include this variety of digital book sales. The list runs in Thursday's edition of USA TODAY and online at booklist.usatoday.com.Rankings for USA TODAY's Best-Selling Books List are based on retail sales data collected each week that include more than 2.5 million volumes from about 7,000 physical retail outlets in addition to books sold online. USA TODAY's list ranks titles regardless of genre or format, providing one of the best assessments of which books are most popular among readers and consumers each week. USA TODAY's Best-Selling Books list has been published each Thursday in the newspaper's Life section since October 28, 1993.