Straight from AE
AuthorEarnings reports analyze detailed title-level data on 33% of all daily ebook sales in the U.S.
30% of the ebooks being purchased in the U.S. do not use ISBN numbers and are invisible to the industry’s official market surveys and reports; all the ISBN-based estimates of market share reported by Bowker, AAP, BISG, and Nielsen are wildly wrong.
Full link:
http://authorearnings.com/report/jan...rnings-report/