• Mitt Romney, Stuck in a Moment

    by  • August 2, 2012 • 0 Comments

    The latest electoral vote forecast is unchanged at Obama 337 – Romney 201, but with today’s update, the uncertainty in those estimates decreases a bit. The main reason is another round of state polls showing Obama maintaining his lead in pivotal states like Florida, Pennsylvania, Ohio, and Wisconsin. But just as importantly, new polls in safe Romney states – including Arizona, Missouri, and North Dakota – also show no consistent up- or down-trends.

    Taken together, these polls let us not only be more confident in current estimates of Obama’s standing, but also in the overall stability of the race up to this point. One of the ways my model projects forward to Election Day is by assessing the past volatility in voter preferences. If and when the polls begin to indicate more instability in voter preferences, more uncertainty will go back into the forecast. As I mentioned the other day, however, an unusually large proportion of voters are already saying they’ve made up their minds. It’s not as if nothing’s happening out on the campaign trail – only, none of it’s moving public opinion.

    The bottom line is that Mitt Romney is facing a very large uphill climb right now. Every major survey aggregator is in agreement that Obama is ahead in current state-level polling – and many see the number of states in the tossup category dwindling. HuffPost has Obama at 290 electoral votes, with only Florida, North Carolina, and Virginia as tossups. Not to be outdone, TPM puts Obama at 310, with just two tossups – Virginia and Colorado. RCP is less aggressive, but still shows Romney needing to (nearly) run the table.

    To put things in perspective, Romney could win Indiana, North Carolina, Colorado, Virginia, New Hampshire, Florida, and Iowa, and still lose the election. For Romney to rebound, something will have to happen over the next three months to either win over decided Obama supporters, or make undecided voters break overwhelmingly away from Obama – which evidence suggests could be a challenging proposition.

    Q2 GDP Growth Released

    by  • July 27, 2012 • 2 Comments

    The BEA released their first estimate of Q2 GDP growth today: 1.5%. This has been the key piece of missing information for the structural forecast I use as the starting point for my model. Until now, I’ve been relying on the Q1 growth rate, which is less strongly correlated with the election outcome. Starting with the next site update (either today or tomorrow), I will switch over to the model based on Q2 growth.

    It’s helpful to have this new data point, but don’t expect a huge adjustment to the forecast. The Time-for-Change model using Q1 growth predicted that Obama would receive 52.6% of the two-party vote. With Q2 growth coming in at 1.5%, the baseline forecast falls all the way to… 52.3%. And this is before factoring in any adjustments from current polling.

    In fact, the next update is also going to incorporate some important new polls. Two in particular stand out. First, we get a long-awaited reading in highly-competitive Missouri. The last polls in that state were done in late May/early June, and suggested a slight Romney lead. This latest survey indicates Romney is actually a few points farther ahead. Second, a poll in Illinois corroborates expectations of a large Obama lead there. So even though the forecast in Illinois won’t change that much, our certainty in it will increase considerably.

    Stay tuned…

    How to Follow the Campaign

    by  • July 26, 2012 • 1 Comment

    Campaign reporters like to speculate about how events today will affect public opinion tomorrow. It’s the main way they justify why some new campaign tactic, news item, commercial, misstatement, gaffe, etc. is “important” or “matters” for the election. I appreciate that this is their job. But if public opinion is what we care about, why not just look at it directly? We have the data. So what are the polls telling us?

    State-level presidential polls are now coming in at a rate of about one or two a day. And what’s happening is: Nothing. Voter preferences have been almost completely stable for nearly three months. The Obama lead we picked up on at the end of June is holding. The poll aggregators over at HuffPost Pollster and TPM are seeing the same thing. Nate Silver called it “The Incredibly Steady Presidential Race”. He’s right.

    It wasn’t like this in 2008. In 2008, polling data showed a series of long-term, up-and-down trends in voters’ preferences for Obama vs. McCain. Support for Obama gradually declined all summer (leading to a bunch of “worried Democrat” stories like this one – really, one of my favorite genres of political reporting), then picked up around the Democratic convention, dropped off again following the Palin VP pick, and finally increased after the September financial crisis. Nothing like that has happened so far in 2012.

    The question, of course, is will it? We still have three months to go. I’d be shocked if nothing happened between now and November. John Sides wrote about the primary factors to watch. But there are three considerations to keep in mind. First, even in relatively “volatile” 2008, voter preferences, by state, typically ranged just five to eight percent from their highest to lowest point over course of the campaign. Second, there are indications this year that an unusually large proportion of voters have already made up their minds. Voters are also saying they don’t have much more to learn about the candidates. Factor in (third) that current preferences are already very close to what the historical model is predicting, and we could be very nearly set.

    Campaign news is entertaining, and it often feels like things that happen should matter. Don’t pay a lot of attention to the speculation. Watch the numbers. I’ll keep updating the site every few days. When public opinion starts to move, I’ll catch it. Then we can go back and look at what might have been the cause, and what it might mean going forward.

    Just to Clarify

    by  • June 30, 2012 • 0 Comments

    Any forecasts about future events are necessarily out-of-sample inferences that are going to be heavily model dependent – particularly in the absence of a lot of historical data, which is the case here. I’ve created a statistical model that aims to apply existing political science research in a systematic, quantitative way, rather than reverting to intuition or other untested “mental models.” The reason I set up this site is to share what I’m seeing in the data, in the context of the model. There just aren’t a lot of opportunities to do this; presidential elections only come along every four years.

    Political scientists don’t often venture into forecasting, but sometimes they do, and sometimes they’re wrong. One of the things that’s different about my approach is that it’s dynamic. If the historical factors I’m looking at right now turn out to be pointing to the wrong outcome, then my forecasts will update from new polls later. The model worked with the polls from 2008, but if it doesn’t work in 2012, I’ll use it as an opportunity to reexamine the modeling assumptions, see what went awry, and refine the approach for next time.

    To reiterate, especially at this early stage in the campaign: All of the forecasts on this site depend on my (informative) priors. I describe how I came to them here. If you also trust those priors, then the probabilities I’m reporting follow from the model and the current polling data. I did my best to calibrate the uncertainty in those priors using polls from the 2008 election. The point is, the outcome probabilities shown on the site should not be treated as “universal.” With different priors, you’d get different forecasts. If you really don’t agree with my priors, don’t worry. The priors will matter less and less as the campaign goes on, and we see the results of more polls closer to Election Day.

    And the model isn’t just for forecasting. It also gives estimates of the state-level trends in preferences for Obama vs. Romney. These trends depend on the polls and the model specification, almost not at all on the forecast priors. As a result, they should be accurate even if the forecasts they’re leading to aren’t.

    A final note: Gallup reported one additional presidential approval poll for June, so I’ve made a minor adjustment to the baseline forecast. In their poll ending on 6/24, they had Obama at 46% approve to 48% disapprove, for a difference of -2%. Averaging this into their other June polls brings Obama’s net rating down from -0.4% to -0.8%. As a result, the Time-for-Change forecast falls slightly, from 52.7% to 52.6%. I’ll be using this as my baseline from now until the Q2 economic data are released.

    Sensitivity to Prior Assumptions

    by  • June 28, 2012 • 1 Comment

    One of the key ways in which my forecasts could be wrong at this stage in the campaign is in the specification of prior beliefs over each state’s election outcome. These are the baseline historical forecasts I start out with, before updating from more recent polls. I’ve chosen to base my priors on a structural model that expects Obama to win 52.7% of the national major-party vote in 2012; or 1% less than what he received in 2008. As I wrote yesterday, this is already a fairly large margin of victory. It’s the main reason the model is producing probabilities of Obama’s reelection over 95%.

    But what if the historical forecast is off? To answer this, we can run the model using a baseline forecast lower than the 52.7% I’m putting my faith in now. Suppose we had reason to believe that Obama’s national vote share will fall by 2%, down to 51.7%; or by 3%, down to 50.7%.

    At 52.7%, we get what’s currently showing up on the site: a 97% chance of victory for Obama, with a median electoral vote forecast of 328.


    At 51.7%, Obama’s probability of winning falls to 89%, with a median forecast of 314 electoral votes.


    Finally, at 50.7%, Obama’s probability of winning is still, perhaps, surprisingly high: 81%, with 303 electoral votes.


    What’s sustaining these chances is how well Obama has consistently been doing in the state polls. According to current estimates, Obama is way ahead in states like Pennsylvania, Oregon, Ohio, and Wisconsin. He also has the lead in closer states, such as Virginia, Michigan, and Colorado.

    Let’s make one more comparison. Over at FiveThirtyEight, Nate Silver does a very similar electoral vote simulation to compute the probability of an Obama or Romney victory (although based on a very different model). Here’s his histogram as of today.

    It actually looks fairly similar to my current simulation results (the first histogram above), with a 10% spike at 332, and a 4.5% spike at 303. The big difference with his is that there’s almost nothing in between! Instead, he finds a long left tail, with Obama having a small but consistent probability of winning anywhere from 270, down past just 150 electoral votes. That’s Bob Dole territory.

    It’s this extended left tail that lets Silver conclude that Romney has even a 35% chance of winning right now. Silver also calculates his electoral vote forecast as the mean, rather than the median (as I do) of his simulation results. This is how he gets a forecast of 292.3 electoral votes for Obama. If he used the median, it would quite a bit higher. And if he filled in that empty space on the Obama side of the histogram, I imagine his probabilities of an Obama reelection would be pretty close to mine.