when free e-books are offered for a relatively long period of time, without requiring registration, print sales will increase
I don’t think the conclusion of this paper can be generalized across other book types (academic ones), but it’s a worthwhile read.
The present study indicates that there is 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 increased sales. This result may be surprising, both to those who claim that when a free version is available fewer people will pay to purchase copies, as well as those who claim that free access will not harm sales. The results of the present study must be viewed with caution. Although the authors believe that free digital book distribution tends to increase print sales, this is not a universal law. The results we found cannot necessarily be generalized to other books, nor be construed to suggest causation. The timing of a free e-book’s release, the promotion it received and other factors cannot be fully accounted for. Nevertheless, we believe that this data indicates that when free e-books are offered for a relatively long period of time, without requiring registration, print sales will increase.
See full article HERE. (thanks to Patrice and Indian/sarai connection).