Actually, I think we probably want them to document *their* confidence, which we will then alter based on some magic heuristics (taking into account some kind of user karma rating, for example).

I would say "how confident are you that this data is accurate, taking into account the quality of the original data, assumptions you have had to make in the scraper, and your confidence in the thoroughness of your scraper?"

I strongly feel we should be asking for user-defined confidence on a much smaller scale, maybe 1 - 4, but we can worry about that later.