Princeton Election Consortium

A first draft of electoral history. Since 2004

Weekend Nerdery (Basic level, part 1): Make Your Own Senate Prediction!

September 20th, 2014, 11:15am by Sam Wang

Some of you may think that analyzing polls is some kind of wizardry. It’s not.

This is the first of a few Basic posts. I’ll have Advanced posts too for extreme PEC aficionados. As always, I reserve the opportunity to make minor corrections. [Read more →]

→ 3 CommentsTags: 2014 Election · Senate

Senate Conditions Are Back To September 3

September 19th, 2014, 4:30pm by Sam Wang

As of today, conditions in the battle for Senate control are just about back to where they were on the day after the shake-up in the Kansas Senate race. Using polls alone in a 2-3 week window (see right sidebar), current medians show the following key margins: Alaska D+5%, Colorado D+2%, Iowa D+0.5%, North Carolina D+4%, and Kansas I+5.5%.

In an election based on today’s polled sample, the most likely outcome is 51 votes for Democrats and Independents.

[Update: see comments. At the moment, significant drivers of the difference between PEC and other sites appear to be (1) we're using all polls, including partisan ones, which changes Alaska; and (2) we're using Kansas two-candidate matchups and don't have fundamentals to drag those polls in the GOP direction.]

The first four races are critical for either side to win control, and among the closest of races this year. Money and time would be very well spent there, for both Democrats and Republicans.

There seems to be a fuss over today’s snapshot probability. It’s only there for rookie readers. The far more interesting and informative quantity is the Senate Meta-Margin, shown above. The Meta-Margin is defined as the amount of swing needed to create a perfect tie for Senate control.

In this calculation, Democrats+Independents=50 is scored as Democratic control because Democratic Vice-President Joe Biden, who presides over the Senate, would be able to cast a tiebreaking vote. If you do not like that assumption, subtract 0.83% from the Meta-Margin to assign Orman to the Republican caucus, or subtract 0.41% to split the difference.

The core assumptions of the Princeton Election Consortium calculations are: (1) to take a snapshot, accept all polls; and (2) the future will resemble the range of snapshots taken since June 1 (after accounting for the Kansas shake-up). Today’s change is an example of  a swing toward the upper end of the expected range, which is between R+0.2% and D+2.5%, peak-to-peak.

→ 53 CommentsTags: 2014 Election · Senate

Scotland Referendum Fails, Surpassing Polls

September 19th, 2014, 10:21am by Sam Wang

The Scotland referendum on independence has failed by a margin 10.6%. Why was this margin so unexpectedly large?

A few days ago, I pointed out that “No” was ahead of “Aye” by 4.0 ± 1.3 % (5 surveys; 1 sigma uncertainty, p=0.014). Later surveys didn’t change that. It is incontrovertible that the polled demographic was against – but was closely divided. What changed? [Read more →]

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How Our Predictions Work (continued)

September 18th, 2014, 7:20am by Sam Wang

Mr. Sullivan, this post is for you.

Even though Nate Silver has misinterpreted what PEC did in 2010 as representing how we operate today, I see this as an opportunity to explain how we make predictions in 2014. I will then come back to a point that many readers will care about more: the assumptions put into this kind of prediction can add hidden biases, whether intentional or not. [Read more →]

→ 41 CommentsTags: 2014 Election · Senate

Meanwhile, in real news…

September 17th, 2014, 8:33pm by Sam Wang

1) Currently, the critical race for Senate procedural control (i.e. whether Dems+Inds keep 50) is in Iowa. Braley’s up by a median of 1.0% over Ernst. That alone is driving the daily snapshot most strongly. Iowa. Is. Important.

2) Scotland is voting on independence tomorrow. “No” is ahead by 4+/-1%. For such a consequential question, that’s very close!

That is all.

→ 12 CommentsTags: 2014 Election · Politics · Senate

How Our Prediction *Really* Works

September 17th, 2014, 11:10am by Sam Wang

I hear that the Princeton Election Consortium calculation has come under criticism for being statistically overconfident. I think there is confusion here, which requires a little explanation – and an appreciation for what I’ve learned since I started doing this in 2004. Basically, after 2012, any predictive calculation started to build in Election Day uncertainty. By conflating a 2010 snapshot with the 2012/2014 predictive model, Nate Silver has made a factual error.

The key difference is between the snapshot and the prediction. Our snapshots are precise because they give a picture of conditions today. Our November prediction builds in the possibility of change occurring in the coming seven weeks. Thus the November prediction above (today at 70%) will, in the near future, usually be less certain than the snapshot (today at 80%). As a reminder, the predictive model is documented and is open-source.

I explained this in 2012. As an example, when our current prediction method is applied to past Presidential races, they gave a cliffhanger in 2004, and clear Obama wins in 2008 and 2012. A polls-only approach suggests that this year, Senate control is also a cliffhanger, with a slight advantage for Democrats+Independents.

I’m sure there are more points I have missed. Have at it in comments. Please be nice about everyone, including any rival sites. Nonsubstantive and rude comments will be moderated.

(Note: while we were down, my response was here.)

→ 55 CommentsTags: 2014 Election · Senate

Will momentum encounter the Queen?

September 16th, 2014, 4:00am by Sam Wang

Last week I pointed out that most surveys indicated that the Scottish independence referendum is unlikely to pass. Nonetheless, a close look suggests that Thursday’s election will be extremely close, thanks to the elusive quality of political momentum. [Read more →]

→ 14 CommentsTags: Politics

Monday morning – Senate steady, House on the move

September 15th, 2014, 9:09am by Sam Wang

Good morning! From a polling standpoint, there was little genuine news over the weekend. However, other sites are moving toward the Princeton Election Consortium estimate. There are several likely reasons. [Read more →]

→ 55 CommentsTags: 2014 Election · House · Senate

CNN, Smerconish, 9:40am Eastern

September 13th, 2014, 8:27am by Sam Wang

Off to caffeinate. [Update: video here.]

→ 20 CommentsTags: 2014 Election

A note on Scottish independence

September 12th, 2014, 4:06pm by Sam Wang

Next Thursday, the people of Scotland will vote on an independence referendum. What’s going to happen? [Read more →]

→ 14 CommentsTags: Politics