@Madness - I'd suggest against it, but it would probably generate interesting discussion. Like I said before, though. I think the hypothesis has a lot of variables to account for.
Please, freestyle with me. I'm not sure I can look at this situation thus far and isolate hypotheses or account for relevant variables.
Well, I assume the point of contention is 'does a fan forum help book sales, harm books sales, or have no effect?' So one would probably want to look at book sales for an author before, during, and maybe even after (less important, probably) having a fan site. And then compare this to sale trends for other authors.
But there are a lot of other reasons a book may or may not sell. I'm hardly a researcher or economist, but I imagine below might be a few things to account for.
- General economic trends. I would think entertainment spending would be lower during bad periods.
- Prominence of the author. If an author has prior success, I assume it increases future sales, which might need to be looked at when comparing to other authors and prior sales.
- Marketing and publicity. I assume different publishers have different marketing ability to some degree. As well as the authors own willingness to travel for tours or reach out to people on the internet.
- Book price. I'm not entirely sure how such a thing is determined, but the price of hardback and paperback varies both between them and between individual books. Could influence sales a tad. One might be able to add something like cover art in here too, but that's getting a bit more into why people buy specific books.
- Nearby releases. If George R.R. Martin is releasing a book, it could affect sales of one author, given prominence of other interests in the genre.
- Accessibility of the fan site. Since I think Lawrence mentioned it, is it a subreddit, is the site linked often? Does it come up high on Google results? If people see the site as often as they might see other mentions, it'd probably have diminishing returns.
Anyway, I think these various things could affect sales and/or analyzing the relevant data trends to isolate effects.