On November 5, 2008 I wrote a post calling attention to the predictive markets. Intrade has since caught a lot of public attention, but I was writing then about the Iowa Electronic Markets, and I still prefer them. Three races is far from statistical validity, as good as they have been, so this year’s a chance to add another data point. Can they make it a fourth good prediction? Let’s review.

Two days before the 2000 election

Who will win
Al Gore – 27.3%
George Bush – 74.9%

Vote Share Prediction
Al Gore – 49.6%
George Bush – 49.4%

Actual result
Al Gore – 48.4%,
George Bush 47.9% – Winner

Two days before the 2004 election

Who will win
George Bush – 55.2%
John Kerry – 45.3%

Vote Share Prediction
George Bush – 51.7%
John Kerry – 48%

Actual result
George Bush – 50.7% – Winner
John Kerry – 48.3%

Two days before the 2008 election

Who will win
John McCain – 11.2%
Barack Obama – 88.3%

Vote Share Prediction
John McCain – 47%
Barack Obama – 53.5%

Actual Result
John McCain – 45.66%
Barack Obama – 52.92% – Winner

2 days before the 2012 election

Who will win
Mit Romney – 29.1%
Barack Obama – 71.8%

Vote Share Prediction
Mit Romney – 48.0%
Barack Obama – 52.8%

Actual Result
? – We’ll find out Tuesday.