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 →]
September 19th, 2014, 10:21am by Sam Wang
September 18th, 2014, 7:20am by Sam Wang
— Robert D Sullivan (@RobertDSullivan) September 17, 2014
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 →]
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.
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.)
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 →]
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 →]
September 13th, 2014, 8:27am by Sam Wang
Off to caffeinate. [Update: video here.]
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 →]
September 12th, 2014, 8:55am by Sam Wang
This morning I’ll be on with Brian Lehrer to talk about poll math, the suspenseful Senate race, and when to accept a bet. Tune in!
[Update 11:23am: that was fun. However, I just found out that Silver claimed that at PEC we use "arbitrary assumptions." OK, that is an out-and-out falsehood. We use polls only and are completely open-source. I do not think a polls-plus-fundamentals outfit like FiveThirtyEight should be throwing that particular stone! -Sam]
In other news, the Senate Meta-Margin’s holding steady at D+1.0%. The Meta Margin’s a better number to watch than the probabilities because it shows how much the race would have to swing to create a perfect toss-up situation.
D+1.0% reflects the close margins at present in a polls-only view. Look at the right sidebar – the top five races are all within 2%. Click on them for rich poll goodness, courtesy of HuffPost!
[Read more →]
September 9th, 2014, 6:20pm by Sam Wang
The Election Day prediction for Senate control is now fully live. There are parts that may require further tinkering, especially concerning how the results are displayed. But it’s basically in place.
Those of you who followed PEC in 2012 will recognize all the components. Basically, I have adapted the Presidential model for the Senate. Here I will document key components that are needed for the Election Day prediction. [Read more →]