Intrade usually takes into account the fact that they’re mutually exclusive, and doesn’t require additional margin for additional candidates (I haven’t seen this documented anywhere, but it seemed to behave that way in the last election).
Still, Intrade’s margin rules aren’t as good as those of the big commodity futures exchanges. Interest rate futures have asymmetrical risk, but that doesn’t distort prices because little margin is required and they’re liquid enough that you can cut your losses before prices change too much.
I’m puzzled about why people preferred the spokesman version of paranoid debating to the initial version where the median number was the team’s answer. Designating a spokesman publicly as a non-deceiver provides information about who the deceiver is. In one case, we determined who the deceiver was by two of us telling the spokesman that we were sufficiently ignorant about the subject relative to him that he should decide based only on his knowledge. That gave our team a big advantage that had little relation to our rationality. I expect the median approach can be extended to confidence intervals by taking the median of the lows and the median of the highs, but I’m not fully confident that there are no problems with that.
I have more comments about Sunday’s game here.