Illegal download sites for the MythTV book

In the last week, I have discovered three download sites offering illegal downloads of the MythTV book e-book. If I can find three without really trying, I assume there are a lot more of them out there. This raises a question for which I don’t have a good answer. Do illegal downloads of books increase, or decrease sales? I can see arguments either way, but I’m tending towards the belief that they don’t increase sales.

Does anyone out there have any data which isn’t merely anecdotal? Want to share it?