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Recently I introduced a simple model for predicting election results from current polling averages and past polling errors. This post presents final predictions for all statewide presidential, senate, and governor's races. This is the first test of this experimental model.

A simple polling average is shown for each race, which includes polls from the entire month of October for races with little apparent change, and polls from the past 10 days for races that appear to have trends in the month of October (including all Presidential races).

The regression prediction is based on a regression of data from 2004-2010 showing the error of the polling averages in a given state is correlated to Obama's 2008 performance in that state. See here for details.

The state-based prediction adjusts for polling errors specific to that state in races from 2004-2010. For example, if in a given state, polls overestimated the Democratic margin by 3 points in a 2008 Governor's race, 2 points in a 2006 Senate race, and 1 point in a 2010 Senate race, the current polling average for a Senate race would be adjusted downward for the Democrat by 2 points. State-based predictions use past Senate and Governor's errors for Senate and Governor's races, and past Presidential errors for Presidential races, because of state/federal party misalignment in some states.

Clarification: positive numbers mean the Democrat wins.



The Governors

The polling average in Montana is very close, but in the 2006 Senate race, polling showed Tester ahead by about 4-5 points, and the final margin was actually only 49-48. (The state-based prediction takes this information into account.) Mason-Dixon showed it tied, however, and they also correctly predicted the 2004 Governor's race. They currently show the Republican ahead by 3.



The Senate

The Senate is more interesting. Both the regression and state-based prediction put the competitive Massachusetts and Connecticut races into the Safe Dem category (+5 or more). The close race in Montana, again, is nudged into negative territory. Meanwhile, the Nevada race is moved from favoring the Republican to favoring the Democrat based on the lousy performance of Nevada polling in recent elections. Note also Hawai'i gets a huge bump in both predictions. And finally I will note I believe there is a significant chance of poll failure in Arizona, where most of the polls have not included enough Latino voters. I would not be surprised to see a very close race there.



The President

These polling averages and predictions are all likely to be off, given the movement in the Presidential race we've seen in the last few days. Nevertheless, rules are rules, so I kept a 10-day average. Looking at the numbers, despite the hullabaloo from the Republicans, PA, NV, and WI are bumped into safe territory by both prediction methods. New Hampshire and Iowa are both nudged downward in the state-based prediction based on local pollsters that, in the past, have vastly overestimated Democratic performance (UNH and Des Moines Register).

Potential Pitfalls
The biggest problem that could cause failure of the models is failure of the polls. With response rates less than 10%, do polls work anymore? We will see. More specifically, the regression model should perform worse when local pollsters are active in a state. Sometimes they may be more accurate or less accurate, but they would be different from the typical mix of national pollsters. In theory the state-based prediction should catch this. But the mix of pollsters may change from one year to the next in any given state. Another way the state-based prediction could fail is in cases where it is based on a limited number of polls. Finally, campaign strategy should be able to alter the relationship between polls and outcomes and could also provide error for this method.

Evaluating the Results
I will consider either model a success if the average absolute error is lower for the predictions than for polling averages alone. Only races with three or more polls will be included in the evaluation.

More fine print.
The state-based model was based on averaging the difference between the polling average and the actual outcomes in elections held between 2004 and 2010. All polls from October were included unless a clear trend was apparent, in which case only polls from the final 10 days were included. A poll with the majority of its field dates within the final 10 days is counted as being taken in the final 10 days. Elections with third party candidates >5%, recall elections, Research 2000, and Strategic Vision were excluded. In cases where four or five polls were within a reasonable range and one poll had a margin more than 20 points different, the outlier was removed. Presidential elections were treated separately from Senate and Governor's races because of misalignment problems in some states (such as West Virginia); however, in most states, the error for the presidential polling numbers is similar to the errors in Senate and Governor's races. Previous races are included in the state-based averages when they have more than five polls. If the state has no races with more than five polls, races with fewer than five polls are used in the average.

Addendum: The House
While I'm at it, I figured I may as well make a prediction for the House too. Based on recent elections, I will guesstimate the generic House vote margin will be +0.5 points more favorable for the President's party than the Presidential margin. But what will the President's margin be? Again, based on recent elections, I guesstimate the polling average plus 1.0 points for the winner. That's Obama +2.4. I'll average that with Nate (+2.6) and Sam (+2.2) - which gives me 2.4 for the President. Which leads to 2.9 for the House. Which leads to a prediction of a 28-seat gain based on my model after adjusting for redistricting. But don't get excited - this prediction has a range, too, of approximately 14-35 seats gained. I wouldn't be surprised if the final result is more towards 14 - but then, with House polling rather sparse this year, nothing would be too surprising.

It's been a wild ride this cycle - we shall see what we shall see!

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Comment Preferences

  •  This is good stuff (0+ / 0-)

    but do you still think Obama is going to win?

    I swear all of this stuff needs that in big bright letters today.  

  •  Looks like you worked real hard on it (1+ / 0-)
    Recommended by:
    Alibguy

    and I appreciate that, but I'm not seeing where the predictions are. I'm an artard sometimes. Forgive me.

    •  The predictions (0+ / 0-)

      The two right-hand columns have predictions under the two different methodologies of adjusting the polls to account for past errors.

    •  But Hey! (0+ / 0-)

      Don't feel bad if most of this analysis goes over your head. Me too. I'm like, what's a regression? Isn't that what happens to the economy after the Repubs have been in charge for a while?
       ;-)

      But us liberal arts types can puzzle out some meanings. For example, the first table, for Governors, lists 7 contested states, including IN.

      Indiana is not easily polled, because of a law banning robo calls. But it is an interesting case in this election, since the Repub Senate candidate decided to tell the truth about what he thought about rape, women's rights and lack thereof, God's Will and all that. Maybe some of that mess rubbed off on the Repub candidate for Gov.

      So the first column in that Gov table shows results averaging a mere 6 polls with the Repub leading by 8%. It then presents the numbers massaged in two ways. The regression doesn't make any difference. But the state-based forecast suggests that the Repub is only ahead by 5.5%.

      It's a lot easier to overcome a lead of 5.5% than a lead of 8%. And with things shifting so rapidly in the Senate race polling, there just might be momentum developing for the Democratic candidate for Gov.

      Of course, it's likely our guy will lose by around 5.5%. But if he closes the gap for a narrow win, you won't have to exclaim, I never imagined that could happen! It probably won't happen, but it just maybe could.

      So, look at the other tables in the same way and you might squeeze out some more info, without having to go back to college.
       ;-)

    •  Sorry - (1+ / 0-)
      Recommended by:
      MichaelNY

      I was called away unexpectedly. Don't feel bad about not being able to understand this post. It's a dense piece that was not written for a general audience. If it works, I'll use the model as a basis for user friendly posts in the next cycle. And thanks to Woody for stepping in, although there's one correction I must make. Positive numbers in the tables above mean the Democrat is winning.

  •  The problem (1+ / 0-)
    Recommended by:
    Woody

    with all of this is the lack of data frpm two cycles with two large polling misses 1996 and 2000. In 2000 Nine states were off by 4 or more percent including some as many 7. This means the data set for most analysis is actually not reflective of true volatility.  The problem is most don't have state data before 2002. It took me months to get state level data for 2000 1996 and 92. When you get that data you realize the fundemtal mistakes that their data create

    True volatility is farhigher than the 2002 to 2010  would lead you to believe
    I  poll watching today so I have an excuse for typos thtime

    The bitter truth of deep inequality has been disguised by an era of cheap imported goods and the anyone-can-make-it celebrity myth - Polly Toynbee

    by fladem on Tue Nov 06, 2012 at 09:49:41 AM PST

    •  Well, I'd like to see (0+ / 0-)

      The polling for 2000 would be good to include, simply to increase the amount of data being used.

      I wouldn't want polling for 1996 or 1992 because the three-way races introduce a huge variable into the polling that is not present in most elections.

      For that matter, I have a hunch that 2002 had a lot of one-time only trends due to 9/11. Remember, 9/11 "changed everything" -- at least in the votes in the next election, when Democrats took a hit in a mid-term election, greatly violating the historic record. So I'd venture that 2000 election data is 'more normal' than 2002 data.

  •  I got too excited (1+ / 0-)
    Recommended by:
    MichaelNY
    Which leads to a prediction of a 28-seat gain [in House seats] based on my model after adjusting for redistricting. But don't get excited - this prediction has a range, too, of approximately 14-35 seats gained. I wouldn't be surprised if the final result is more towards 14 ...
    iirc, We need 27 seats to restore Speaker Pelosi to her rightful place, and to put the then-former Budget Committee Chair Paul Ryan on the discard pile where he belongs.

    Whew. I may need a cigarette after reading this forecast, however hedged it might be -- and I never smoke. (Tobacco.)

    Looks like I will be up very late, waiting for returns from CO, TX, AZ, NV, and CA, to see if we got the 27 seats we need.

    •  Sorry... (2+ / 0-)
      Recommended by:
      Woody, MichaelNY

      Didn't mean to get you involved in drugs.

      For the House, there's just a lack of information. I can tell you this - the generic ballot tends to follow the presidential margin lately. If the presidential returns appear very tight, we certainly will not win the House. If, on the other hand, returns appear to be conforming to polls, then it's possible but not likely. If Obama appears to be outperforming the polls, start counting House seats - you may be in for a long night.

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