Predictions about a Supreme Court ruling bear no resemblance to predictions about election results. Markets like this work by "pricing in" information relevant to the prediction. The Supreme Court is, effectively, a black box: until a decision is released, there is very little information with which to make a prediction. With an election, on the other hand, there is an almost endless stream of information one can use to: polls (even skewed polls provide useful information, as long as the internals are released), economic data, other external indicators, etc.
See no. 19.
“Markets like this work by “pricing in” information relevant to the prediction”
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Paul Ryan Intrade chances: 4.1%
BTW, where do you think Intrade would be if they saw the early voting # s from OH?