> * They have low but non-negligible probability, like whole percents to tens of percents
That doesn't seem to be a good range - markets like Intrade are known to have long-shot biases, and the more restricted the range, the less attractive it is as a market. (It's harder to find irrational traders to take for 10 or 20% return if there are only a few prices it could trade at! Now something like Obama for President where the prices could range from 0 to 100 at various times, that's worth trading.)
> * They have low but non-negligible probability, like whole percents to tens of percents
That doesn't seem to be a good range - markets like Intrade are known to have long-shot biases, and the more restricted the range, the less attractive it is as a market. (It's harder to find irrational traders to take for 10 or 20% return if there are only a few prices it could trade at! Now something like Obama for President where the prices could range from 0 to 100 at various times, that's worth trading.)
@gwern: Thank you very much for sharing this!