Princeton Election Consortium

A first draft of electoral history. Since 2004

CNN with Candy Crowley: Sunday 9AM (and noon)

October 25th, 2014, 8:27am by Sam Wang


Tomorrow morning, I’ll be on CNN’s State Of The Union with Candy Crowley. Other guests are Newt Gingrich, Stephanie Cutter, and Stu Rothenberg. Tune in!

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Senate horserace update: what does a Meta-Margin of R+0.4% mean?

October 23rd, 2014, 6:00pm by Sam Wang


Update, Saturday: with two new surveys in Alaska, one showing a tie and the other showing a Begich (D) lead, the predicted Senate Meta-Margin is D+0.0%, a perfect tossup. Statistically this is not different from the minuscule difference yesterday…but it does emphasize how closely fought the battle for control is. To see more, click on the seat graph at the right or the Meta-Margin graph.

Now that Greg Orman (I-KS) has a median lead of 1.5%, the Senate Meta-Margin has gone to R+0.4%. For those who are new, let me explain what this means. [Read more →]

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Do governors face an anti-incumbent wave?

October 22nd, 2014, 12:05am by Sam Wang


TNR essay:
In my new essay in The New Republic, I analyze gubernatorial races. The bottom line: there are lots of extremely close races, mostly involving embattled Republican incumbents. These difficulties for the GOP are a lot like what Democratic Senate candidates are experiencing: the need to defend gains made in a previous wave election.

At this point, the median outcome is a net gain for Democrats of one governorship. This does not fit with the idea of a Republican wave. Read on!

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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!

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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 →]

→ 34 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.

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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.

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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 →]

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