Princeton Election Consortium

A first draft of electoral history. Since 2004

Sunday 9:45am – on MSNBC’s Up With Steve Kornacki

October 18th, 2014, 7:21pm by Sam Wang


OK, we rescheduled from last week. The topic tomorrow: elections and poll nerdery. The Senate obviously, but perhaps the House and governorships too. Tune in tomorrow!

…and, here’s the video. It was fun, fairly substantive, I described the incredible power of Iowa voters compared with my puny vote in New Jersey (at the moment, 1 Iowa vote > 100 Jerseyvotes). Best of all, there was hardly any nerdfighting!

→ 8 CommentsTags: 2014 Election · Senate

Midterm National Senate Polling Error Is Five Times Larger Than In Presidential Years

October 17th, 2014, 12:49pm by Sam Wang



Yesterday, Nate Silver and I both examined Senate polling errors. He saw no overall bias; I pointed out that recent bias has been unusually large. Both statements are true. But neither of us pointed out that the biases follow a significant pattern: midterm-year polling is far less accurate than Presidential-year polling.

From a practical standpoint, this is good news for those of you who don’t like where things have headed lately: in midterms, Senate polling errors are five times larger than in Presidential years. There is bad news too: the error can go in either direction, and a GOP blowout is also possible.

I am interested in why midterm errors are so large. In midterm elections, voter attention is lower than in a Presidential year. In 2012, the Presidential campaigns of Barack Obama and Mitt Romney were in the news every day. This year, it’s…Ebola, which I am pretty sure none of you will ever get. Yet Ebola is in the media much more than any of the aspirant Senators, Representatives, and state officials who will affect our lives. I would guess that more of my neighbors know there is Ebola in Texas than know that Senator Cory Booker is up for re-election.

With lower voter attention comes lower turnout – and evidently, lower certainty about which voters will show up to vote. Other distractions take away from the important issue of Joni Ernst’s desire to eliminate the Environmental Protection Agency…hey, pay attention, I’m talking to you! Ebola Ebola Ebola! There, now you’re back. Thank you.

Here, let me show you how bad the error is. [Read more →]

→ 30 CommentsTags: 2012 Election · 2014 Election · Senate

The Problem With Polls, or…Are Senate Democrats Really Doomed?

October 15th, 2014, 11:49pm by Sam Wang


TNR essay:
Here at PEC, the calculations are built on the assumption that on average, polls provide an unbiased measure of eventual Election Day behavior. This assumption is our strength and our Achilles heel, and it is the topic of my new piece at The New Republic. The supporting calculations are here.

In the 2010 and 2012 elections, Democrats outperformed state-level polling medians by an average of 2.7 to 3.7 percentage points. That’s a substantial jump from previous years. To put this in perspective, the Senate Meta-Margin, defined as how far opinion would have to swing in close races to make Senate control a perfect toss-up, is currently R+1.3%. A polling error of 2.7-3.7% would reverse that margin. I have no idea if such a large error will happen this year. That would require knowing the reason(s) for polling errors, which could be multiple. However, the fact that it has happened in the last two election cycles does make a person pause. For this reason, the probability in the banner is a fairly soft number.

Usually there are 3-4 tight Senate races per year. At this point the playing field has expanded to seven: Colorado, Iowa, Georgia, North Carolina, Louisiana, Arkansas, and Kansas. These are critical for both sides. See the ActBlue and NRSC links at left.

Update: over at FiveThirtyEight, Nate Silver takes a long view, examining all Senate polls from 1990-2012. It’s a good piece of work. However, I think a more appropriate calculation for the current situation would be to focus only on races won by close margins, since polling errors are greater in blowouts, and biased toward the winning party. He and I get very different results for 2010, which makes me suspect that a deeper look at close races would be interesting. He posted his numbers; if anyone cares to delve into this more, I’d be interested in seeing (and sharing) the results.

Update 2, 5:00pm: Maybe Silver and I have both missed the true pattern: midterms vs. Presidential years. In his results, the median absolute error in Presidential years is 0.65 ± 0.6% (SEM). In midterm years, the absolute error is 2.9 ± 0.7%. These are different (p=0.03). The difference is even larger if one replaces his 2004-2012 numbers with my close-race data. Basically, midterm polls can very plausibly be off…but in which direction?

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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 →]

→ 36 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