Princeton Election Consortium

A first draft of electoral history. Since 2004

Halloween story: The Curse Of The Midterm Polls

October 31st, 2014, 12:05am by Sam Wang


Senate polls in individual states have moved around…but the Meta-Margin and the average seat count have stayed stable. Nonetheless, the crystal ball is cloudy. Why is that? The midterm polling curse.

As I wrote last week, everyone’s calculations are, to an extent, built on sand. Historically, in any given year midterm polls have been off in the same direction by a median of 2 or 3 percentage points. Depending on the year, either Democrats or Republicans end up outperforming polls. In current poll medians, six races are within less than 2 percentage points: Alaska, Colorado, Georgia, Iowa, Kansas, and North Carolina. Therefore all six of these races could be won by Republicans…or all six could be won by Democrats.

The other races total 48 Republicans and 46 Democrats/Independents. Republicans are slightly favored to take control, since an even split of the six close races would give them the 51 seats they need*. However, the likely possibilities range anywhere from a Republican majority of 54-46 to a Democratic majority of 52-48. As of today, cranking through the math and the uncertainties gives a probability of 55% for a Republican takeover.

I am thinking about how to guess on Election Night where in this range the race will land. Here are my current thoughts. After feedback, I may turn them into a printable scorecard. [Read more →]

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Iowa and Colorado: Is early voting showing up in polls?

October 29th, 2014, 9:43am by Sam Wang


Over at FiveThirtyEight is a new essay saying that there hasn’t been any concerted movement during this campaign season. Broadly, I agree with their objection that journalists and pundits overuse (and thoughtlessly use) the word “momentum.” However, in this case a close look at the data suggests there was strong movement from September through early October – which then stopped or reversed slightly.

The movement is easier to see in a polls-only snapshot, which is what is published here. In particular, Iowa and Colorado moved toward Republicans throughout September – and in the last few weeks, moved back toward Democrats. One possible cause is early voting – which should show up in surveys. [Read more →]

→ 64 CommentsTags: 2014 Election · Senate

Overreacting to Ebola

October 28th, 2014, 9:24am by Sam Wang



The amount of Ebola coverage is amazing: 1,869 stories from October 20 to 24 alone. That coverage came on the heels of the death of one patient in Dallas, Texas. The level of coverage is amazing considering the far greater impact of other infectious diseases in the United States: rotavirus, which kills dozens of small children every year; West Nile virus, a similar number of adults; and of course influenza, which kills thousands even in years when there is no epidemic. One way to look at this is to calculate the ratio of stories to deaths. It’s about 6 million times higher for Ebola than for influenza.

Ebola appeals to our fears: the disease is grisly. It is a serious threat with tremendous public health implications – in western Africa. That is the reason for sending relief workers overseas – fighting it there so we don’t have to fight it over here. Unfortunately, popular intuitions about it are often wrong. Many people seem unaware that asymptomatic individuals are not contagious, and the disease is not transmitted by airborne means. It is unfortunate that more coverage does not focus on evidence-based information such as this New England Journal of Medicine editorial.

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In State Races, As Much Suspense As 2006 and 2010 Combined

October 26th, 2014, 11:21pm by Sam Wang



Journalists and pundits have lavished considerable attention on the question of who will control the Senate in 2015. But a broader phenomenon has escaped notice: the sheer number of close state-level races, both in the Senate and in statehouses. At risk are many incumbents who were elected in previous wave years: in 2010 for Republican governors and in 2008 for Democratic senators. [Read more →]

→ 29 CommentsTags: 2014 Election · governors · Senate

CNN with Candy Crowley: Sunday 9AM

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


On SOTU with Newt Gingrich, Stephanie Cutter, and A.B. Stoddard. Tune in! [transcript] [CNNgo until Tuesday - scroll back to the 9 AM hour and it’s the last segment, named “Down to the Wire and Up for Grabs”]

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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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