Tag Archives: forecast model

Emory University political scientist Drew Linzer, who created and runs the Votamatic website, paid a visit to Middlebury College last Wednesday to discuss why, based on his forecast model, he believes President Obama is still the heavy favorite to win the presidential election.  To construct his model, Drew uses his colleague Alan Abramowitz’ “Time for A Change”  forecast model as his baseline starting point.  You will recall from one of my earlier posts that Abramowitz’s forecast model uses three factors — the incumbent president’s net approval rating at the end of June, the change in real GDP in the second quarter of the election year and a first-term incumbency advantage — to predict the winner of the national popular vote.  However, during the current election cycle Abramowitz updated his traditional model to include a “polarization” variable that, in effect, reduces the advantage enjoyed by a first-term incumbent running for reelection by about half – from a bit more than 5% to closer to 2.5%.  Under his “new” model, Abramowitz projects Obama’s share of the two-party vote to be about 50.3%.

As I’ve discussed before, not everyone accepts Abramowitz’s rationale for updating his model.  Drew is one of the skeptics, and so his forecast model starts with the “old” Abramowitz model which is decidedly more bullish regarding Obama’s chances.  Without the polarization variable, Abramowitz’s structural baseline component has Obama winning 52.2% of the two-party national vote.  That’s a much stronger starting advantage for the President than the “new” Abramowitz model suggests.

The second component in Drew’s model is the state-based polls, which he uses to “update” the Abramowitz baseline forecast. As we get closer to Election Day, state-level survey data influences his projection more and more, and Abramowitz’s structural component becomes correspondingly less important.  At this point, 10 days out, the state-level polling component is really driving his forecast almost entirely.

So, where does the race stand, according to Drew’s model?   As I discussed in my Economist post, as of today, he projects Obama to win 332 Electoral College votes, or 62% of the 538 Electoral College votes, compared to Romney’s 206.

Note that Drew makes several assumptions in his model.  First, he makes no effort to adjust for the “house effects” of individual polls in the belief that in the closest states that are polled most frequently, polling biases will largely cancel out.   Second, he essentially assumes that the “undecideds” will break in rough proportion to the distribution of the vote, as indicated by the polls, in each state.  Third, since he is interested in forecasting the Electoral College vote, he pays no attention to national tracking polls.

It is doubtful that Drew, or anyone, could have constructed such a forecast model even eight years ago.  But the proliferation of state polls, particularly in contested states, now allows political scientists to adjust their structural models in light of recent polling on a state-by-state basis.   Of course, this type of modeling is in its infancy; Drew only has one previous election cycle, in 2008, to calibrate his assumptions.

I asked Drew what would happen if he changed his baseline starting point by, for example, substituting Doug Hibbs’ Bread and Peace forecast model, which predicts that Obama will win closer to 47% of the two-party vote – or about 5% below the Abramowitz projection.  Drew acknowledged that this would shift the baseline parameter enough to move several swing states into Romney’s column.   Nonetheless, based on a state-by-state electoral projection and given the current polling, even with this shift Drew does not believe that Romney would gain enough Electoral College votes to overcome Obama’s current projected advantage.

Is Drew right?  Remember, for some time now I have been arguing that the state-level polls will gradually align with the national tracking polls, which as of today are showing a much closer race, with some indicating that Romney has pulled into a narrow lead.   How much must Romney gain in the key swing states to overcome Obama’s polling lead? Using the RealClearPolitics state polling averages, Owen Witek created the following table showing the state of the race in the 12 closest state races as of today (Electoral College votes are in parentheses). The last column contains an estimate of the number of undecided voters in each state.

Source: Real Clear Politics, 10/27/12

Based on the RCP averages (and remember that Drew’s state-based polling formula includes a structural component and thus is different than the RCP simple averaging), Obama right now has 201 Electoral College votes in strong and lean states, compared to Romney’s 191. That leaves 146 electoral votes in the 11 swing states listed in the table still up for grabs.  How likely is it that Romney can pick up the additional 79 needed to reach 270?  If he holds his “lead” in Virginia, North Carolina and Florida, he picks up 57 more, leaving him with 22 to go. Assuming a small shift in voter sentiment, he might also squeak to victory in Colorado, earning another 9 electoral votes, leaving him 13 to go.

But here is where the math becomes difficult for Romney, and why Drew – as of today – believes Obama will hold on.  Obama leads by more than 2% in all the remaining battleground states.  His smallest lead is 2.3% in three states: Ohio, Iowa and Wisconsin.  Looking only at these three, Romney needs to win either Ohio, or Iowa and Wisconsin, to reach the 270 mark.   But, as Witek shows, there are not very many undecideds left in either Iowa or Wisconsin, so they would have to break strongly in Romney’s favor for him to eke out a victory in both states.  That means Ohio may still be Romney’s best path to victory, and that assumes Obama loses the other states – no sure thing.  Remember, Romney got perhaps a 2.7% boost from the first widely-watched debate that was generally viewed as a convincing win for him.   How likely is it that he will be able to almost match that total in the last 10 days among the much small number of undecideds in the absence of a similar focusing event?

Keep in mind that all these calculations are based on polls that are, by nature, very squishy, so we ought not treat the RCP averages as having more precision than they do.  In this respect, Drew’s model, which uses a different algorithm to analyze the polls and predict the final outcome in each state, presents a slightly different picture in the battleground states.  Here are Drew’ state-based calculations, complete with the 95% confidence interval.  (Note the cool color coding!). As you can see by the vertical line in the middle demarcating the 50% threshold, he projects that Obama will do slightly better in key states than a simple reading of the RCP polling averages might suggest.  In contrast to my simple RCP average, he has Florida, Virginia and Colorado all leaning toward Obama (although with a confidence interval that suggests Romney might be leading in all three states).  That means Romney has that much of a bigger hill to climb among the undecideds.

Of course, if Romney does begin to close the gap in the swing states, Drew’s model will pick that up, and it will adjust the forecast accordingly.   Regardless of the outcome, however, there is one overriding reason why you should be visiting his site for the next 10 days: in contrast to other forecasters (you know who I mean), Drew’s methodology is completely transparent.  Anyone can see and utilize his modeling equation, which he describes at length in this journal article  (which has been peer-reviewed and accepted for publication). Moreover, as an academic, Drew’s rooting interest in this race is to see whether his forecasting tool is validated. He has much less at stake if the model turns out to be wrong. If it is wrong, however, he can tell us why.  I call that progress.

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