Free ebooks' effects on book-sales

Simon sez, "John Hilton, a doctoral candidate in Instructional Psychology and Technology at Brigham Young University, crunched the numbers to determine whether releasing books through Creative Commons and other methods really does benefit authors and publishers. He found that four titles recently released for free by Random House saw an 11 percent increase in sales in the eight weeks after releasing the online copies compared to the eight weeks prior."
For his research, he has located, so far, approximately 40 book titles for which publishers have released free online versions at least eight weeks after releasing the printed version. He does not consider books that were released both simultaneously for free online and as print products because then he wouldn't be able to observe the before and after effects on sales. He then records the Bookscan numbers -- which account for about 70% of all US book sales, including those sold at most retailers -- for the eight weeks prior to the free release and the eight weeks after.

On March 4 of this year, Random House announced that it would release five books for free through its science fiction portal, all of which came in downloadable PDF files (among other formats). Hilton recorded the before and after book sales and found that "one of the five books has had zero sales in 2009. So no sales before or after the free version. But the other four books all saw significant sales increases after the free versions were released. In total, combined sales of the five books were up 11%. Together they sold 4,633 copies the 8 weeks prior to being released free and 5,155 copies the eight weeks after being released."

Did Random House's free online book releases affect sales? (Thanks, Simon!)