PredictWise Blog

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.

PredictWise went into Election Day with 27 elections that had a non-negligible probability for both candidates. Of those elections 20 or 74% moved more Republican; the bias was 1.8 percentage points and the average absolute error was 2.2 percentage points. Much of this was driven by Maryland where the error was 9.9 percentage points! The gubernatorial elections had a bias of 1.6 percentage points (1 percentage point without Maryland) and the senatorial elections had a bias of 1.9 percentage points.

The interesting thing is breaking the group up into likely Republican and likely Democratic. In 13 of 14 elections that leaned Republican, the Republican did better than expected. In the remaining 13 elections the Republicans did better than expected in 7 of them. Actually, without Maryland, the Democratic leaning states had no bias, and tiny average absolute error of 1.5 percentage points.

What does this all mean for traditional polling and voting? That is the puzzle that we will explore over the next few weeks and months.

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.

The overall average of the 71 elections was 93%, translating into an expected outcome of 66 correct elections. Which means we were relatively well calibrated at 66. In short, we won one more senatorial election than we should and loss one more gubernatorial election than we should.

House (419 of 435): There are still several house election in dispute, but assuming the current leaders prevail, our house election were 419 of 435. The average probability for the leading party was 96% which translates into an expected correctness of 417 seats. So, we are relatively well calibrated at 419 seats. Only two of the sixteen “misses” went Democratic versus Republican.

All “misses” in the senate, governor, and house elections, except for two house races, went Republican rather than Democratic. So the Republicans over-performed the predictions overall.

Election Night 2014

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

10:33 PM ET:

10:13 PM ET: We have the senate at 95% for the Republicans, but that almost feels generous to the Democrats.

8:07 PM ET: The Democrats continue to over-perform the trandtional polling in the exit polling (with the exception of VA, which is tight). And, they are all but certain to capture both of the key must wins states of NH and NC. Georgia is tighter than expected as well. This is going to to be long night, but definitly better for the Dems than expected. 

7:34 PM ET: We just upgraded NC to 95% in light of the strong exit polls for the incumbent Hagan. VA is too tight to call right now, which is bad new for the Democrats. But, both GA elections are too close to call as well, which is bad news for the Republicans. Overall, the Democrats are slightly over-performing on the exit polls relative to the traditional polling. But, it is too early to say if the results are going to be biased in either direction this election cycle. Grab a snack, becuase the roller coaster at 8 PM ET!

6:36 PM ET: Kentucky has closed a part of the state and the early returns have GOP incumbent McConnell well ahead of 2008 in almost every location. He went into tonight at 100% and will win

3:20 PM ET:

1:30 PM ET:

1:15 PM ET: The table below will update all night tonight and all commentary by me will be in this spot. So, please check back for live updates starting just before 7 PM ET.

Link to House page ...

Note: Prob is "probability of victory" and EV is "expected vote share"

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. Please take a look at this post on the mission of Microsoft Prediction Lab.

First, we would like the thank the thousands of active users who made this first game such an interesting and meanignful experience!

Microsoft Prediction Lab has a market for all 507 elections in the midterms: 36 senatorial, 36 gubernatorial, and 435 house. In each of these markets users can buy and sell contracts on the possible outcomes of each election. For example, in New Hampshire there are two possible outcomes: Democratic candidate Jeanne Shaheen and Republican candidate Scott Brown. A prediction on Shaheen would return 112 points for every 100 wagered, while a prediction on Brown would return 467 point for the same 100 points! If someone thought that Brown as undervalued, that there was a good return in wagering 100 points for 467, s/he should predict Brown and if s/he thought Shaheen was undervalued they should buy Shaheen. As people predict Brown, the return goes down and vice-versa.

The return that an investment settles on in a market is extremely correlated with the probability of the outcome. We show the translation of the price to the probability on the market alongside the return on prediction.

Further, the markets moved quite a bit over the last few weeks. Actually, there was movement in most of the 507 markets. In this market 85 people placed predictions, while others saw well into triple digits. To test how efficient that movement was, whether the crowd was supplying information, we captured the probabilities in all 507 races at about midnight on Election Eve.

These probabilities represent the probability of victory for the party just before 12:00 AM on Election Day. We look forward to checking back later this week to see how Microsoft Prediction Lab did ... and, for those of you playing the game, you have until 9 PM ET to keep the predictions coming!

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:

2 Tough, but possible pickups for the Democrats:

Wisconsin: this is a potentially a huge pick-up for the Democrats against a likely 2016 contender for the Republicans. Scott Walker is a conservative Republican leader in a solid blue state.

Maine: Paul LePage is a second unapologetic conservative Republican in a solid blue state. He is also in a tight spot.

3 Likely pickups for the Democrats:

Florida: neither the Democratic former governor Crist nor the current Republican governor Scott are pulling ahead in this nail-biter.

Alaska: independent Bill Walker (running with a Democratic lieutenant governor) is looking very strong against the Republican incumbent.

Kansas: Paul Davis is pulling ahead of conservative Republican Sam Brownback in this incredibly red state.

3 Likely holds for the Democrats:

Colorado, Illinois, and Connecticut: all three of these have looked tight, but are likely to remain blue governors in blue states.

1 Likely hold for the Republicans:

Michigan: this is a generally blue state, but there is a Republican incumbent heading towards a likely hold.

1 Likely loss for the Democrats:

Massachusetts: the only likely bad mark on the election for the Democrats is Martha Coakley. She is poised to lose against a moderate Republican Charlie Baker. Although, as a moderate Republican in a state with a long tradition of moderate Republican governors*, this is not a major ideological shift. *Note: I am referring to Governor Romney, a moderate, who should not be confused with Republican nominee for present Romney, who is not a moderate!)