It's implied in his belief that the 3.5% probability is an over-estimate. He says that estimate is 'clearly wishful thinking of Ron Paul supporters'. If that is true then Ron Paul supporters must either be more prone to wishful thinking than supporters of other candidates (if everyone was equally prone to wishful thinking then the biases should cancel out) or more likely to participate on Intrade. Either or both of these hypotheses may be true but I'm curious what the reasoning is.
Depending on taw's theory to explain the Ron Paul bias he may be able to identify better arbitrage opportunities. If he believes that Ron Paul supporters are over-represented on Intrade for example then he should seek out other venues to place the other side of the bet to take advantage of the hedging opportunity described by Blueberry. Identify a venue where supporters of other candidates are over-represented and seek someone to take the bet at what he believes to be fair odds or at odds that underestimate Paul's chances. Pocket the spread whoever wins.
He also suggests that Ron Paul supporters are trying to artificially pump estimates for Ron Paul and are willing to write off losses as a marketing expense. If this is more true for Ron Paul than it is for other candidates' supporters then that suggests Ron Paul may have more dedicated supporters or wealthier supporters, both of which are tendencies that should in fact raise his probability of success given the nature of the US political system. Is he factoring that information into his own estimates?
Given your first paragraph, I think your question answers itself: his evidence is the 3.5% figure, which (for reasons unspecified) he considers an obvious overestimate.
There is something rather odd going on in this discussion, whose structure is as follows. A indicates belief in proposition p; B notices that p => q; B challenges A to supply evidence for q. This seems to presuppose that A's belief in p is actually derived from a prior belief in q, since otherwise p would be the proposition to ask for evidence of; but when asked, B claims that s/he is onl...
I've noticed something very curious on Intrade markets for 2012 Republican Presidential Nominee - Ron Paul gets 3.5% of getting a nomination - a value that's clearly (and spare me EMH here) wishful thinking of Ron Paul supporters more than any genuine estimate.
And this brings me to a question - if prediction markets overestimate chance of winning of some rare case, how can I profit from that? Naively if I know true chance is 1%, I win $3.5 99% of the time, and lose $97.5 1% of the time, for expected payoff of $2.5. But my maximum loss is 39x higher than my expected profit, and I won't be getting any money out of it for three more years.
I'd need to bet significant amount to earn any money out of it, and that would require accepting 39x as high maximum loss. No reasonably prediction market would accept this kind of leverage without some collateral, nor could I get any reasonable loan for it at rates that would make this arbitrage profitable.
The only way I can think of would be convincing someone with plenty of money that I'm right, and have him provide me with collateral for some (probably very high) portion of the payoff. But if results depend on my ability to convince rich people, that's not prediction market! None of this is a problem for people trying to artificially pump estimates for Ron Paul - they'll just take the loss, and write it off as marketing expense.
None of these problems occur if some position is vastly overestimated, like 60% estimate if I know true value to be 40% - this would be a cheap bet - maximum loss of $40 for expected profit of $20, and people who want to pump it need to take about as much risk as people who want to bring it back to the true value, not a lot more.
I'm confused. Is there some nice way to arbitrage this, or is this an inherent weakness of prediction markets and we should only trust positions they pick as leaders, not chances of their long tail?