Princeton Election Consortium

A first draft of electoral history. Since 2004

Brief notes

October 14th, 2014, 10:36am by Sam Wang

We’ve been experimenting with presenting the probability as a decimal, on the grounds that the false precision of showing the ones-place is misleading. For example, “0.4″ means 40%. However, I’m not seeing a lot of love in comments about this change – a bit of a mixed reaction.

Note that the uncertainty (1 sigma) on the probability is at least 0.15, or 15% (and it’s asymmetric; more uncertainty in the D direction). For this reason, aggregators should not be showing a ones-place in the percentage; you don’t see “39%” in weather forecasts, and those are about as accurate as what we’re doing. We could also show it as ”40 +/- 15%”.

If you want to see the precise forecast of many aggregators, they’re all available at The Upshot (NYT). They just added PEC – many thanks to Josh Katz and the team there. The calculations all point in the same direction, a very gentle lean toward Republican control. However, everyone’s using the same polls, so a polling error would make us all wrong. Ponder that!

I’ll say it again – 60% is not that certain. If you flipped a coin weighted like that in favor of heads, 2 out of 5 times it would come up tails. The show’s not over.

Update: PEC’s November win probabilities are here, as well as piped over to the NYT.

→ 52 CommentsTags: 2014 Election · Senate

Early voting picks up steam

October 12th, 2014, 8:48pm by Sam Wang

Early voting has started, most notably in Iowa, Florida, and North Carolina. Here is a rundown by Michael McDonald, who drills into the subject in amazing detail. While we’re at it, here’s his early voting tabulation page. Bookmark it!

P.S. For general comments use the MSNBC thread. There’s a great conversation going on there.

→ 30 CommentsTags: 2014 Election

MSNBC, Sunday 8:45am with Steve Kornacki

October 11th, 2014, 8:22pm by Sam Wang

On Sunday morning around 8:45am, I’ll be on MSNBC’s Up with Steve Kornacki. Update: Pre-empted by Ebola! On my mind at the moment:

In the Senate, recent Iowa polling leaves us with a median of Ernst over Braley by just 0.5±0.8% (8 polls), a dead heat. Also, what’s up with Colorado and South Dakota? Finally, look where the NRSC is putting money. A big tell that they see things the same way as we do in The Power Of Your Vote (see the right sidebar). Bottom line, Democrats+Independents seem headed for between 48 and 51 seats. Suspense!

In the House, voter sentiment is more like 2012, not the wave year of 2010. Republicans will retain control for sure, but we don’t know who will win the popular vote.

Democrats appear to be positioned to pick up a few governorships. Five races are currently within one percentage point (FL, WI, ME, KS, IL), and four of those are held by Republicans.

What’s on your mind?

→ 57 CommentsTags: 2014 Election · Senate

Everything is different today…or maybe not!

October 10th, 2014, 9:53am by Sam Wang

At this moment, PEC’s probability of D+I is 49%. Yesterday it was 52%. Obviously everything is different, a volte-face. Right? Um…

Only if you don’t have a clear understanding of uncertainty. This is common among even the most experienced journalists [NPR] [WaPo]. It makes the baby Ronald Fisher cry.

For a refreshingly accurate and insightful look at how to think about knife-edge probabilities, Mark Mellman has written an excellent article for The Hill. [Read more →]

→ 20 CommentsTags: 2014 Election · Senate

No Wave

October 9th, 2014, 11:35am by Sam Wang

Today let’s back up a step, and not focus so much on individual polls, or even single races. A larger picture emerges if we look at recent polls in the Senate and the House, as well as President Obama’s net disapproval rating.

Taken in full, polls indicate a continuation of recent polling trends: a House that looks a lot like 2012, and at least three Senate races within a single percentage point (IA, CO, KY), with control of the chamber going either way in November. Overall, Republicans are still headed for a good year in the Senate, driven in large part by the fact that many Senators who are up for re-election ran in 2008, a Democratic wave year.

There is one piece of genuine news, which concerns the Kansas election. [Read more →]

→ 38 CommentsTags: 2014 Election · House · President · Senate

Poll geekery on All Things Considered and MSNBC

October 7th, 2014, 4:06pm by Sam Wang

NPR interviewed me and my lab members here at Princeton. It was fun, and it did get across that polls-alone might be enough. However, it didn’t have time to focus on one nuance, maybe because it’s a bit dull: PEC and other sites are not that different in their predictions. We’re talking one or less Senate seat of difference on average, well within the uncertainties. It’s just that Senate-2014 is a close election. It aired on NPR’s All Things Considered at 4:20pm, 6:20pm, and 8:20pm Eastern. This should work: [link to audio]

Update: Wednesday night on MSNBC’s The Last Word with Lawrence O’Donnell. The topic: Greg Orman of Olathe, Kansas. It’s archived here].

→ 15 CommentsTags: 2014 Election

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 →]

→ 78 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