Somebody arbitrage and fix please

I've been explaining to folks 'round the office why we might wish to pay more attention to iPredict's markets on who will be Prime Minister than to the vote share markets. And I thought I might share it with you.

National's back up over 70% in the PM.National contract. If National wins, that contract pays $1; if they lose, it pays $0. It dropped into the 60s last week during the publicity around the Hager book, but it's now back up.

But, if we look at the major party vote share markets, it's hard to see how National could possibly be 73% likely to win. National's predicted to get 43% of the vote; Labour and the Greens are predicted to get 43% of the vote; minor parties get 14%. While NZ First may be more likely to go into coalition with National, Internet/Mana isn't, and Conservatives' wasted votes, if they get 4.4%, disproportionately waste votes that otherwise would have gone to National.

There's a bit of a problem in all the vote share markets though. You can only bring so much money into iPredict at a go, and folks might there be liquidity constrained. The winner-take-all markets can then just be more interesting. The VS markets, paying off at a penny for every percentage point earned by the party in the election, give little chance of large gains or losses. You can sink a whole pile of money into that market to get maybe a cent or two's return on a 43-cent investment. It's not all that great. The PM markets provide a less certain return, as there's bigger chance of large losses if your expectation of the probability is wrong or if the wrong side of the weighted coin turns up, but the 70 cent investment either gets you a dollar or it gets you nothing.

How can we tell that it's the continuous payout structure? iPredict also has a market where the National Party vote share pays out in buckets: one contract pays $1 if the vote share is over 43% (and $0 otherwise), another at $1 if the vote share is over 43.5%, another for 44% and up, and so on through 49%.

In the vote share (continuous) market, you pay $0.43 for a contract giving you $0.01 for every percentage point of the National vote. In the vote share (discrete) market, at current prices, you would pay $0.90 for a contract paying out at $1 if National gets more than 43% of the Party Vote. You'd pay $0.83 for a contract paying $1 if National gets more than 44% of the Party Vote. You'd pay $0.67 for a contract paying $1 if National gets more than 45% of the Party Vote. You'd pay $0.59 for a contract paying $1 if National gets more than 46% of the Party Vote. 46.5% is at $0.55 and 47% is at $0.48. So the market, in those bucketed contracts, expects National to get between 46.5% and 47%; the parallel Labour ones have Labour getting between 28% and 29%. That's rather more consistent with a 70% chance of National's forming government.

But watch for Winston. NZ First is at 4.8% in the standard vote share market, but he's also odds-on to take more than 5.5% of the vote. The Conservatives only have a 29% chance of topping 5%.

Somebody with time ought to go in and fix things so there isn't free money sitting between the bucketed and continuous vote share markets.