That’s the subject of a study conducted by John Hilton III and David Wiley, both of Brigham Young University.
Their study was based on sales records for 41 books within three groups and notes sales records 8 weeks before the free digital release and books sales 8 weeks after the free digital release. The complete study and conclusion is available here: http://quod.lib.umich.edu/cgi/t/text/text-idx?c=jep;view=text;rgn=main;idno=3336451.0013.101
After listing to all the pros and cons of giving away e-books to generate print sales, I found it interesting that one of the conclusions in this study is that there was a “ … moderate correlation between free digital books being made permanently available and short-term print sales increases. However, free digital books did not always equal increase sales.”
About the authors:
John Hilton III received his M.Ed. from the Harvard Graduate School of Education and currently is a Ph.D. student in Instructional Psychology at Brigham Young University. He is interested in researching open-access issues, particularly the creation and use of open educational resources, and looking at how free digital book distribution affects print sales and the impact of books.
David Wiley is an associate professor of Instructional Psychology and Technology at Brigham Young University.