Princeton Election Consortium

A first draft of electoral history. Since 2004

Political science model matches PEC long-term forecast

October 7th, 2014, 3:55pm by Sam Wang

In TalkingPointsMemo is a rundown of political-science models of this year’s Congressional campaign. Such models are research tools that use pre-campaign fundamentals to test a hypothesis about how a campaign “ought” to turn out.

Today I point out that the Highton/Sides/McGhee Senate forecast has, in some sense, already been confirmed: it is essentially identical to PEC’s long-term forecast, which was based on polls from June to now. In that sense, the TPM article didn’t mention a pretty interesting fact: the match between our polls-only analysis and at least one non-polls-based model. [Read more →]

→ 11 CommentsTags: 2014 Election · Senate

A Reply To Nate Silver – With Factchecking

October 6th, 2014, 8:19am by Sam Wang

Political Wire:
This post:
In response to the “Twitter-crit” post below, Nate Silver wrote a longer piece for Political Wire. There’s also this interesting analysis by Daniel Altman at The Daily Beast.

This Monday morning, I replied in Political Wire. Check it out.

I thank PEC readers Bum, bks, Froggy, Kevin, AySz88, Hugh J Martin, Art Brown, Alan Koczela, Lojo, 538 Refugee, Philip Diehl, Amit Lath, and A New Jersey Farmer for advance comments on the essay.

→ 70 CommentsTags: 2014 Election · Senate

Peer review…by Twitter?

October 1st, 2014, 2:00pm by Sam Wang

I’ve been an author on 70 scientific publications. They all went through a process called scientific peer review, where anonymous reviewers critique a paper and the authors respond. Eventually an editor decides to accept or reject the work. The process can take a while, and the editor’s role is key. My most recent paper, which provided a new way of looking at the biology of autism, had no fewer than five peer reviewers, one of whom was rather hostile. It’s an arduous process!

To my surprise, unfolding on Twitter is an alternate-universe version of peer review. But the analogy is not quite right. The most prominent reviewer’s name is known to me (and to you). In this analogy, you, the reader, are the editor.

In my experience, only a handful of strategies get a result through peer review successfully: (1) point-by-point response to every critique, (2) pointing out factual error by the reviewer, and (3) new data. With that, let me reply.


First, I should say that the best part of this discussion is to focus everyone on the national election. In some ways, the national election in 2014 is the closest electoral question since 2000, Gore v. Bush. This year’s contest is critical for shaping the coming two years in the United States.

To the reviewer: I appreciate the comments. Thank you for mentioning the Princeton Election Consortium (PEC) online. It’s driven up traffic to levels I’ve never seen in midterms before. However, I am concerned that you don’t really understand our current methods. The flavor of the statistical approach comes from physical sciences, and may seem unfamiliar. To step outside the usual peer review process for a moment: it seems like something that could be solved over a beer or two.


There are a few general themes in the critique:

  1. Statements that PEC makes excessively precise statements of probability, focusing mainly on work done in 2010.
  2. A lack of accurate mention of PEC’s actual methods, which we have used since 2012.

There are a number of factual misstatements. Where possible, I will redirect the discussion to how PEC actually works. [Read more →]

→ 77 CommentsTags: 2014 Election

PEC switching (as planned) to short-term forecast

September 30th, 2014, 12:30pm by Sam Wang

[Note, October 13: The probability is currently displayed as a decimal, i.e. 0.4 means 40%. The reason for this is that the precision of the probability is no better than +/-10%. This is the case for other aggregators as well - we're just being explicit about it. - Sam]

As planned for a long time, we’re switching soon to a short-term forecast. As I wrote last month, the Meta-Margin has some predictive value for where it will be within five weeks. The election is in five weeks, so it’s time to start factoring in current conditions.

I’m traveling today, so there will be a slight delay in bringing it live. In the meantime, after reading your comments on yesterday’s thread, I have some comments of my own. [Update: after the break, I have now added a simpler summary.] [Read more →]

→ 32 CommentsTags: 2014 Election · Senate

A change in the air?

September 29th, 2014, 11:58am by Sam Wang

The Princeton Election Consortium’s approach to tracking current conditions has unique advantages, which are sometimes underappreciated and misinterpreted – even by major media figures. The advantages are:

(1) We have remarkably low noise compared with a simpler approach such as at or RealClearPolitics; and

(2) We have sharper time resolution than other sites that use smoothing, whether explicitly or implicitly, to get a more gradual curve over time. Those approaches can’t capture sharp changes as easily. Sites that appear to do this include HuffPollsterThe Upshot, and FiveThirtyEight.

Each site has its own advantages. The unique advantage of PEC’s Meta-Analysis is that it resists outliers – yet also captures real change. In other words, we publish a sensitive and accurate “electoral thermometer.”

In the last 10 days, that thermometer ticked sharply in the Republicans’ direction, past where it’s been at any point this election season. It is not time for Democrats to panic – especially since polls don’t always match final outcomes, even in the home stretch. However, it is time to choose battles carefully. At the end of this piece I will suggest some battles to choose. [Read more →]

→ 59 CommentsTags: 2014 Election · Senate

Midterm traffic – thank you

September 27th, 2014, 9:36am by Sam Wang

Some of you are asking if the PEC polls-only prediction is wrong. I say no: the prediction is OK…so far. Recall the central assumption: the Meta-Margin range from June through now is representative of the future. Obviously, this week it is on my mind that the assumption won’t hold up. However, we’re only a touch below the range I have stated: R+0.2% to D+2.5%. We’ll see very soon. Also, next week, as planned from the start, the PEC model will start incorporating an element of “random-walk-from-the-present.” At that point, any inaccuracy will tend to fix itself – like the other predictive sites.

In the meantime…thank you for reading, both here and at The New Yorker. The Princeton Election Consortium is getting excellent midterm traffic! We’re not far below the level for August-September 2012, which is pretty good considering it’s not a Presidential year.
As you might guess, last week’s dust-up created more traffic…though not that much direct linkback from our friends at the ESPN subsidiary.

In the meantime: watch the banner above, ignore isolated polls, and use the right sidebar…including ActBlue (Dems) and the NRSC (GOPers)!

→ 37 CommentsTags: 2014 Election · Senate

Alaska and Colorado on the move

September 26th, 2014, 3:57pm by Sam Wang

The Meta-Margin is a powerful statistical measure. It collects all available polls into a simple index that tracks movement in the national campaign. No house effects, no fancy stuff – just a measure of national opinion, calibrated using Senate control to define the zero point.

Recall that the Senate Meta-Margin is defined by how much all Senate races would have to swing together in order to create a perfect tied probability for Senate control between Republicans and Democrats+Independents. Yesterday, the Meta-Margin moved by 1.4% toward Republicans. By the standards of this year’s campaign, that is a huge movement. The change was mostly caused by movement in just two states, Alaska and Colorado. Those were ways for Democrats+Independents to hold 50 votes, and as of today, those routes are currently looking unfavorable. Therefore now the Meta-Margin is R+0.1%. That is a near-perfect tie if polls are exactly calibrated to Election Day behavior (is it? that’s a question for another day).

Our time window is currently to take the last 3 polls or the last 2 weeks of data, whichever is more, for each state. This measure takes a little while to move, but when it does, that’s meaningful. Statistically, we are now at the most Republican-leaning end of the range that we have seen in the entire graph.The dip in June looks better for Republicans, but keep in mind that on September 3rd, the Meta-Margin jumped by 0.8% when Chad Taylor (D-KS) dropped out of the race. Subtracting that gives a better feeling for where we’re at, not counting Kansas. In short: as a group, Republican Senate candidates outside Kansas are at an all-time high.

Will this change stick? There is still plenty of time for movement in most of the races listed in the right sidebar (The Power Of Your Vote). Still, we should take the latest change fairly seriously. Alaska was a hidden bonus for Republicans all along, as I analyzed yesterday. But the change in Colorado polls – I’ve been pondering that all week. Something big happened there: a swing from Udall +3.0±0.7% (mean±SEM, 4 polls) to Gardner +4.5±2.2% (4 polls). As a trigger, I nominate the Udall-Gardner debate, which is the kind of event that can move opinion by showing the two candidates side by side.

As usual, recall that The Power Of Your Vote is a list of states where individual votes are most valuable. Those states are where get-out-the-vote activism and campaign contributions will have the greatest impact.

→ 18 CommentsTags: 2014 Election · Senate

Brief update

September 26th, 2014, 8:45am by Sam Wang

In current polling conditions, the Senate Meta-Margin has left Democratic territory for the first time since mid-August. Not much to say about that for now, except that the sharp movement was driven by fresh polls in Alaska and Colorado. If you  have questions, read about Meta-Margins here.

The prediction is described here; it integrates information from June until now. If current conditions persist, it will start to move. Also, starting next Tuesday it will start to emphasize current conditions more, as those conditions start to be more strongly predictive of Election Day. More later.

→ 6 CommentsTags: 2014 Election · Senate

What’s The Real Source Of Inaccuracy In Alaska?

September 25th, 2014, 5:30pm by Sam Wang

On Tuesday, I suggested that control of the Senate could come down to as few as four key races in Colorado, Iowa, Louisiana, and Arkansas. There’s a fifth state where voters are exceptionally powerful: Alaska, because of the closeness of the race and its small population. But even though get-out-the-vote efforts in Alaska are certain to be valuable, activists will have to do their work without a clear picture of which candidate is ahead, Democrat Mark Begich or Republican Dan Sullivan.

As you can see, the Meta-Margin moved toward Republicans today. This is caused by two recent polls in Alaska. This race has had only seven surveys since Sullivan clinched the nomination in August. I think we may continue to see fluctuation in Alaska surveys in the coming weeks. Today I want to point out some special characteristics of Alaska that complicate any exercise in poll aggregation: its small population and extreme mobility in and out of the state. The bottom line is the possibility of polling error like what happened in the Nevada 2010 Senate race…though in the opposite direction. [Read more →]

→ 13 CommentsTags: 2014 Election · Senate

Register to vote **now**!

September 25th, 2014, 6:30am by Sam Wang

Comments OffTags: 2014 Election