Preliminary assessment of the accuracy of the Intrade State-by-State contracts

Now that the election is over, it is interesting to compare the actual outcome with my naive “prediction” method which allocated Electoral College votes based upon a cutoff price point of 55 for the 102 state-by-state Intrade contracts. On the eve of the election (see “Prediction Markets Update: November 3, 2008“), the state-by-state contracts implied a 353-174 Obama Electoral College “lead” over McCain, with Missouri being the only swing state. This morning, according to the Wall Street Journal‘s Interactive Map, Obama has officially won 349 Electoral College votes compared with 163 Electoral College votes for McCain. The actual state-by-state allocation matches mine exactly with the following exceptions:

1. I had Indiana going for McCain; apparently Indiana’s 11 Electoral College votes will instead end up in Obama’s column. This is why McCain’s actual Electoral College vote total is 11 less than what I predicted on November 3. In Indiana, Obama ended up with a 22,986 vote (0.86%) margin over McCain out of 2,681,726 votes cast.

2. North Carolina has yet to be called (although this morning, with 100% of the precincts reporting, Obama currently appears to have a 12,160 vote (0.29%) margin out of 4,191,812 votes cast). If you reduce Obama’s November 3rd total of 353 Electoral College votes by 15 (for North Carolina) and add 11 (for Indiana), this gives you 349 Electoral College votes for Obama.

This morning, the NTH.CAROLINA.DEM and NTH.CAROLINA.REP contracts are trading for 96 and 2 respectively, so it is almost certain that North Carolina’s 15 Electoral College votes will end up in Obama’s column. Furthermore, the MISSOURI.REP and MISSOURI.DEM contracts last traded this morning at 96.5 and 3.2 respectively, so it is almost certain that Missouri’s 11 Electoral College votes will end up in McCain’s column. Therefore, I expect the final Electoral College totals for the 2008 Presidential election to be 364 Electoral College votes cast for Obama, compared with 174 Electoral College votes cast for McCain.

Addendum: November 5, 2008 Electoral College Vote allocation (based upon actual voting data reported by the Wall Street Journal):

Barack Obama (349): California (55), Colorado (9), Connecticut (7), Delaware (3), District of Columbia (3), Florida (27), Hawaii (4), Illinois (21), Indiana (11), Iowa (7), Maine (4), Maryland (10), Massachusetts (12), Michigan (17), Minnesota (10), Nevada (5), New Hampshire (4), New Jersey (15), New Mexico (5), New York (31), Ohio (20), Oregon (7), Pennsylvania (21), Rhode Island (4), Vermont (3), Virginia (13), Washington (11), and Wisconsin (10)

John McCain (163): Alabama (9), Alaska (3), Arizona (10), Arkansas (6), Georgia (15), Idaho (4), Kansas (6), Kentucky (8), Louisiana (9), Mississippi (6), Montana (3), Nebraska (5), North Dakota (3), Oklahoma (7), South Carolina (8), South Dakota (3), Tennessee (11), Texas (34), Utah (5), West Virginia (5), and Wyoming (3)

Not yet called for either candidate: Missouri (11) and North Carolina (15)

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