Polling

A closer look at that GOP over-performance

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There are 35 senate elections (excluding Louisiana) and 36 gubernatorial elections. We had expected vote shares for all of them, in terms of two-party vote share, which were primarily generated from traditional polling.

In 54 of 71 (76%) elections the Republican candidate over-performed (28 of 35, 80%, senate and 26 of 36, 72%, governor). The average error (the bias in one direction) was 2 percentage points (the average absolute error was just 2.8 percentage points). The bias was a little more extreme in the gubernatorial elections (2.3 percentage points), than in the senatorial (1.8 percentage points). Since almost all errors were in the same direction, the absolute error is not much larger than the error.

Overall Calibration Pretty Good ...

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In a preliminary look at Election Eve predictions for the 507 elections, we did pretty well.

Senate (34 of 35): I am going to hold out Louisiana for now and assume there were 35 elections. In those 35 election we had the binary winner in 34 of them, with NC going Republican, despite 85% for the Democratic incumbent. The average probability for the leading candidate was 95%, which translates into an expected outcome of 33, so we overshot by 1.

Governor (32 of 36): I am going to assume that the results in Alaska, Colorado, Connecticut, and Vermont all hold. In all of these elections we were leaning towards the current leader. Florida, Illinois, Kansas, and Maryland all leaned Democratic prior to the election and were captured by Republican. We had an average probability of 92% for the leading candidate going into the election, which translates into an expected outcome of 33, so we undershot by 1.

Election Night 2014

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1:30 AM ET: This is what under-performance versus the polls looks like:

Congress - Likelihood of Party Control - After 2014 Election

2014 Senate - Likelihood of Victory for Democratic Candidate - Election Night

2014 Governor - Likelihood of Victory for Democratic Candidate - Election Night

Microsoft Prediction Lab's final probabilities

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Five weeks ago I launched a new website, with a few friends, including Miro Dudik and David Pennock, called Microsoft Prediction Lab. The website consolidates research into both non-representative polling and prediction games. I have spent years understanding how various raw data: polling, prediction markets, and social media and online data, can be transformed into indicators of present interest and sentiment, as well as predictions, of varying populations. Then, how decision makers allocate resources with the low latency and quantifiable market intelligence that we produce. Microsoft Prediction Lab allows us to continuously innovate not only on the path of raw data to analytics to consumption, but the collection of the data itself.

Microsoft Prediction Lab - Final Probabilities

Democrats poised for (possible) great night … in governors elections

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The Democrats have a decent chance at having a great night in the governor’s races. There are 10 elections that I am following closely:

Republicans at about 85% to capture U.S. Senate

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The Republicans are about 85% likely to take control of the U.S. Senate in January, 2015. This is going to happen, because the Democrats are going to win Blue States and the Republicans are going to win Red States. And, the Republicans are likely going to win two crucial Purple States (Iowa and Colorado). This election is not wave or a disaster for either party, but pretty much as should be expected. The most likely outcome is going to be the Democrats controlling 47-8 seats to the Republican 52-3.

The Democratic path to victory is very simple; they need to capture both New Hampshire and North Carolina, which are likely, and then three additional states of the five in play. The runoff system makes it very unlikely they will win in Georgie and Louisiana. And, I do not think Kansas’ Orman is going to make himself the swing vote with a 49 Democratic senate. Why would he do that if he can switch back in 2017 with seniority when the Democrats recapture the senate?

Hidden Errors and Overconfident Pollsters

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Written with Sharad Goel and Houshmand Shirani-Mehr

Election forecasts, whether on HuffingtonPost's Pollster, New York Times’ Upshot, FiveThirtyEight, or PredictWise, report a margin of error of typically 3 percentage points. That means that 95% of the time the election outcome should lie within that interval. We find, however, that the true error is actually much larger than that, and moreover, polls historically understate support for Democratic candidates.

What do you regard as the most important factor in the health care debate? If I wade into this question, would you prefer to hear more about what the public thinks, what the likely outcomes ahead may be--or what the law itself is likely to accomplish going forward?

What people believe about the likely impact of a given piece of legislation can be markedly different from its actual impact. It seems likely that the Affordable Care Act, if fully implemented, will end up creating benefits for a great deal more than the 18 percent of Americans who think it will based on the new Kaiser Family Foundation poll.

Also, what people want to happen can also be very different from what will happen. At the present juncture, Congress and the White House have very little to say about the future implementation of the health care law; that's much more the province of the courts.

These subtleties are really important if you are planning for the impact of this law on your business--or if you are thinking about campaigning or voting for or against this law.

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Herman Cain is rising in the polls of Republican primary voters, but prediction markets are not buying into the Cain surge. On Wednesday evening, MSNBC led its web page with the breaking news that the network's latest poll showed Cain atop the GOP presidential field, with 27 percent support; Romney was a close second at 23 percent, and Rick Perry placed third with 16 percent.

Yet the prediction markets, where users can buy and sell contracts on who will ultimately win the Republican nomination, are still very skeptical of a Cain victory. The real-time markets assessing the likelihood of the Republican nomination still have Romney enjoying a commanding 65.7 percent lead, with Perry trailing at 12.5 percent and Cain at 10.1 percent. Here is a look at how the leaders have progressed over the last few weeks:

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Polls are important. You see a lot of them during a campaign season. The question is, what do they really mean?

The quoted margin of errors are large and significant. And, the real error is much larger and more significant than the quote margin of error!

Yet, despite this margin of error and the daily fluctuations, polls are a very meaningful source of information in understanding and predicting an election. You just need to be clear on what a poll means and how best to use it.

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