Princeton Election Consortium

A first draft of electoral history

← Presidential prediction 2012 (Election Eve) Presidential prediction 2012 (final… stay tuned) →

Senate prediction 2012 (Election Day final)

November 6th, 2012, 11:00am by Sam Wang 90 Comments -->

Briefly, my predictions are
President: (mode) Obama 332, Romney 206 EV, (median) Obama 309, Romney 229 EV. Two-candidate popular vote: Obama 51.1%, Romney 48.9%.
House: Democrats win 2-22 seats. D 205+/-10, R 230+/-10 seats, Republicans retain control.
Senate: Democrats win 1-3 seats. D/I 55 +/1, R 45 +/- 1 seats, Democrats retain control. More on the Senate here.
The poll-based median Senate outcome is 55 Democratic/Independent seats, 45 Republican seats. It is very focused: 85% of the probability is concentrated in the range of 54-56 D/I seats.


Win probabilities:
>90% Democratic. Connecticut (Murphy), Massachusetts (Warren), Missouri (McCaskill), North Dakota (Heitkamp), Virginia (Kaine).
81-89% Democratic. Indiana (Donnelly), Wisconsin (Baldwin).
71-80% Democratic. Montana (Tester).
75% Republican. Nevada (Heller).
>90% Republican: Arizona (Flake).

Update: Wow, I’m getting it good and hard in comments. I made a transcription error on North Dakota – the probability there is 75%. Sorry!

Also, I should not have expressed these primarily as probabilities. The probability function is a nonlinear function of margin and SEM. That means it (a) can offend intuition, and (b) is susceptible to user error.

In regard to the latter, it would be better for me to add in a possible bias of b=-2% to +2%, as defined before. That slop factor will give a more realistic assessment given poll accuracy. The “slopped-up” probabilities are below.

State (n) median+/-SEM D win%
Arizona (4) Flake +5.5+/-3.8% 12%
Connecticut (8) Murphy +6.0+/-1.3% 99.8%
Indiana (10) Donnelly +2.5+/-2.0% 84%
Massachusetts (8) Warren +4.5+/-2.0% 96%
Missouri (7) McCaskill +6.0+/-2.9% 96%
Montana (5) Tester +1.0+/-1.3% 69%
Nevada (7) Heller +2.0+/-2.9% 27%
North Dakota (3) Heitkamp +2.0+/-2.3% 75%
Virginia (8) Kaine +3.0+/-1.1% 96%
Wisconsin (9) Baldwin +1.0+/-0.9% 72%

Tags: 2012 Election · Senate

90 Comments so far ↓

  • spacer Grateful // Nov 6, 2012 at 11:04 am

    Good morning Dr. Wang -

    That looks about right to me.

    Just voted in Northern VA, took about 2 hours total from start to finish.

    Everyone have a great day!

    • spacer Rebecca // Nov 6, 2012 at 11:32 am

      I have a masters in statistics and find these statistics very reassuring.

  • spacer Kerr // Nov 6, 2012 at 11:07 am

    Thanks for all you do, Sam. I work in data warehousing and analysis, and I appreciate your scientific approach to poll aggregation. I hope, for reasons both scientific and political, that your EVpredictions are as close to the mark as they’ve been in the past.

    Being from MO, I am particularly happy to see a confident prediction for McCaskill. Akin really hurt himself with his comments.

  • spacer Pat // Nov 6, 2012 at 11:08 am

    Sam, both your mode and your median (332 and 309) do not correspond to the current estimators (303 and 312). Are you deviating a little from your own numbers (snapshot and histogram) to make your prediction? Or is it based on an earlier or future update to the topline numbers?

    • spacer SkepEng // Nov 6, 2012 at 11:21 am

      I was thinking the same… How is the mode at 332? It doesn’t coincide with the one in the histogram.

  • spacer Frank Katz // Nov 6, 2012 at 11:10 am

    Check out Intrade. People who put their money where their mouth is are buying Obama and dumping Romney at a furious rate. POTUS is now up 4.5% TODAY. Another confirmation of Dr. Wang’s predictions.

    • spacer Muhahahahaz // Nov 6, 2012 at 11:52 am

      I just opened an account recently, and my money finally got there this morning. Oh how I wished I had opened it sooner!

      I’m not gonna buy “Obama wins” for more than $7 (it’s currently at $7.37+), but there are plenty of other good bets to be had. :-)

  • spacer Paul G // Nov 6, 2012 at 11:17 am

    I am glad about the current Senate outlook, but I have a (pessimistic) question about the long term trajectory of the Senate. Historically, good candidates have been able to win Senate seats all over the country. However, as the parties become more ideologically sorted and the public becomes more partisan, it seems to be getting more difficult to play on the other partys turf. (Recent exceptions due to Republicans nominating terrible candidates notwithsatnding.)

    In the long run, this seems to be a terrible dynamic for the Democrats. According to the Cook PVI, there are 27 lean Republican states and only 22 lean Democrat states. But when you look at the very partisan states, it is much, much worse. 22 states have a PVI of R > +5, while only 10 have a PVI of D > +5.

    Right now the Democrats hold a bunch of seats in deep red states but that could change soon, such as in 2014 when a bunch of them are up for re-election.

    If the Senate becomes better sorted by party, and all the strongly partisan states elect their own type, we cold be looking at a situation where the Republicans start off with around 40 safe Senate seats, the Democrats with only 20, and they fight over the other 40 “middle state” swing seats.

    I hope this is not where we are headed, but I dont see any reason why not…

    • spacer Rieux // Nov 6, 2012 at 11:43 am

      Well… do you expect the Republicans to stop nominating idiots like Christine O’Donnell, Sharon Angle, Todd (actually William) Akin, or Richard Mourdock any time soon?

    • spacer E A Dawsoni // Nov 6, 2012 at 11:47 am

      It’s certainly one of the strongest long-term stressors on current constitutional arrangements, and likely to become more so.

      Medium “long-term”, to some extent even the reddest states will likely become bluer in statewide races as they urbanize – the correlation of population density with voting behavior is a lot stronger than many realize, for example, play with the sliders at:

      setting them to 1-1000 and then 2000 – top of scale, for starters.

    • spacer rich thaler // Nov 6, 2012 at 11:49 am

      in addition to the prospects of Republicans coninuing to nominate hard right misogynistic candidates, demographics will also help reduce or eliminate the Republicans potential in many southern and southwestern states. Black and hispanic growth rates outpace those of white voters. Unless republicans adopt more immigrant and minority friendly policies, as well as more woman friendly policies, they are looking at an increasingly bleak future.

    • spacer John // Nov 6, 2012 at 12:12 pm

      Republicans should have a long term natural advantage in the Senate, Governors and state legislatures as they dominate the low population prairie states.

      Considering that the national vote is basically split along party lines, but Republicans have advantages in the low population states (and therefore have more control over gerrymandering in total), they should have a minor advantage in the House too.

    • spacer Fred // Nov 6, 2012 at 12:51 pm

      Demographics will sort that out. Every year there are less and less angry old white people relative to everyone else.

    • spacer E A Dawsoni // Nov 6, 2012 at 1:41 pm

      For some reason my link above doe not work.

      Instead, Google:

      “county level map election 2008″

      and select :

      “Electoral Explorer – Election Results 2008 – The New York Times”.

    • spacer Steve16748 // Nov 6, 2012 at 1:45 pm

      Good topic Paul, I’m seeing the almost everywhere things are getting bluer, as the old Montana ranch wife said; “progress is made one funeral at a time”. There are 22 to 24 reasonably blue states now, not counting Virginia, Florida, N. Carolina, Montana in that mix. Add in Arizona, Missouri, Indiana, and even Texas as someday blues and we stand a pretty decent chance of majorities in the Senate in the future. Lets have the guts to get rid of the filibuster and get on showing the public that we pass legislation that makes life in America better. It could be a virtuous cycle.

  • spacer skmind // Nov 6, 2012 at 11:20 am

    Dr. Wang, can you please add an event for Hurricane Sandy on your chart(s).

    I want to make sure that people see that the Ro-mentum had died long before Sandy, and that there was a steady, slow rise for Obama since about the middle of October.

    That narrative is going to be played to save punditry over the next month if Romney loses

  • spacer Robin Colgrove // Nov 6, 2012 at 11:20 am

    Just voted as a family unit in Needham Ma for Warren. I’ve been doing door-to-door canvassing for Warren from back when she was _trailing_ in the polls. This was my (college freshman) son’s first vote. He had not gotten around to mailing in his absentee ballot till too late so we drove out last night to Tufts to bring him home to vote. It took some doing but we did convince the (very nice) poll supervisor that since we showed her the unused absentee ballot, it was OK for my son to vote. It made me think that the situation can be much different for people who _don’t_ have friendly, sympathetic poll workers and savvy, determined family on their side!

    • spacer Khan // Nov 6, 2012 at 11:32 am

      Very, very different. Good parenting :D

  • spacer NickP-LA // Nov 6, 2012 at 11:22 am

    Does it really matter that the democrats are controlling the senate? Repubs are filibustering everything.

    • spacer BrianTH // Nov 6, 2012 at 11:26 am

      The exact mix of Democrats elected to the Senate may end up determining whether or not there is filibuster reform (at the end of the day, the filibuster is just a matter of Senate rules).

    • spacer RocketDoctor // Nov 6, 2012 at 11:31 am

      Reid has stated that he was wrong not to do filibuster reform at the start of the last Senate.

      If one is to believe him, we’ll have some filibuster reform in the next Senate. My only fear is that it is faux reform without any teeth. We shall see.

    • spacer E L // Nov 6, 2012 at 12:15 pm

      FYI: The filibuster is a Senate rule, not a US law or part of the US Constitution. A majority vote of the Senate sets the Senate rules at the opening session of each two year term. Once the rules are set for the term it takes a 2/3 to change them. But 2/3rds is only the traditional rule for changing a rule and could be changed at the beginning of the two year term by majority vote.

    • spacer John // Nov 6, 2012 at 12:19 pm

      The time to do filibuster reform was in 2008.

      If he does it now, which I strongly doubt, it will be just in time for the Senate to flip back to the Republicans in 2014 as many vulnerable Dems that won in 2008 come up for re-election in an off cycle year.

      Also, what would be the point of doing it now given that the House is controlled by extreme right wingers? The only thing this would help with is maybe USSC nominations and treaties — in exchange you hand Republicans a club to beat Democrats down with on everything in 2014.

      It would be an extremely dumb move if he did it now. But, of course, he’s a leader of the Democratic Party (my party) so that would be par for the course.

    • spacer Olav Grinde // Nov 6, 2012 at 12:41 pm

      @John, Iā€™m very skeptical of filibuster reform for precisely those reasons. In a future Republican-dominated Senate, filibustering may well be the only way for Democrats to block heinous Republic-sponsored legislation.

    • spacer BrianTH // Nov 6, 2012 at 1:17 pm

      I think there is a very good argument to the effect that the filibuster over the long run serves the interest of those who typically prefer the status quo and, when necessary, legislative inaction. On net, that may w is neither affiliated with the authors of this page nor responsible for its contents. This is a safe-cache copy of the original web site.