Microsoft Prediction Lab tested the wisdom of the crowd in 507 elections this fall and did pretty well (here are the posted final predictions from election eve): 33 of 35 (so far) in the U.S. Senate, 30 of 36 in the gubernatorial elections, and 419 of 435 in the U.S. House. This is in terms of binary outcomes (i.e., who won and loss), but I will get into the probabilities below.
In the senate, there were two reasonable and well calibrated “misses”. The final prediction was 61% that Greg Orman would knock off incumbent Republican Pat Roberts in the Kansas. And, 62% that incumbent Democratic senator Kay Hagan would hold off Thom Tillis in North Carolina.
In the gubernatorial elections, there were six “misses”. The final predictions had challenger, Democrat, Paul Davis overtaking incumbent Sam Brownback in Kansas with 69%. Democratic challengers, Charlie Crist (78%) and Mike Michaud (55%) both failed in their attempts in Florida over Rick Scott and in Maine over Paul LePage, respectively. Everyone missed Democrat Anthony Brown (77%) to beat Lawrence Hogan for the open seat in Maryland. Finally, Democrat Dannel Malloy was 49% to hold off Thomas Foley in Connecticut and Republican Sean Parnell was 78% to hold off Bill Walker in Alaska. These misses are consistent with the top poll-based forecasters, like Nate Silver.
The forecasts for the senatorial and gubernatorial elections were well calibrated. The average probability for the favorite in the senatorial elections was 90%; we expected 32 of 35 to be correct and got 33 of 35. In the gubernatorial election we had an average probability of 83%; we expected 30 of 36 to be correct and got 30 of 36.
With so much information available, we were not surprised to see the prediction games mirror the major poll-based forecasters, that is why the U.S. House predictions are the most exciting; 419 of 435 elections is a very strong track record! It is a little stronger than the expected 409, but we are not complaining. Of the 16 misses, 4 went Democratic and 12 went Republican. This is not so surprising in a year of Republican victories.