Self-Reporting is not always accurate because some authors might report false sale figures.
But I believe most of the authors who self-report on kboards.com/authors are reporting accurate figures.
Even if they only exaggerate a tiny bit in their own favour (and studies suggest that most people will do this), then all the statistics there will be useless.
And as people who are enjoying some success are more likely to report their sales figures than those whose books have failed to sell, the stats are even more skewed.
If there was a dataset available which had been compiled from verifiable numbers by an independent agent, I'd take it seriously. Otherwise, it's just not reliable enough to be anything more than a bit of fun, I'm afraid.
Adam,
you posted links to those blog posts before, and in a thread which has now been locked.
There are two problems with this.
AW is huge. Really huge. It has over 50,000 active members. If everyone started duplicating posts, AW would collapse under its own weight; we'd need to start charging people for membership, because of the increased server costs: it wouldn't be good. So from now on, please remember to post things once only. No duplicates. OK?
The other issue is that the other thread was locked, and for good reason. That means the conversation is over. If you think a thread should be reopened, send the moderator who closed it a PM arguing your case. But don't try to rekindle it in a different thread, or start a new thread to continue that conversation, because that will just get you a ban.