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By Jay Cost

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On Gallup's Two Likely Voter Models

There have been reams of paper dedicated to reporting on the Obama campaign's voter mobilization efforts. This is what the Washington Post wrote on Sunday:

In 2004, Democrats watched as any chance of defeating President Bush slipped away in a wave of Republican turnout that exceeded even the goal-beating numbers that their own side had produced.

Four years later, Sen. Barack Obama's campaign intends to avoid a repeat by building an organization modeled in part on what Karl Rove used to engineer Bush's victory: a heavy reliance on local volunteers to pitch to their own neighbors, micro-targeting techniques to identify persuadable independents and Republicans using consumer data, and a focus on exurban and rural areas.

But in scale and ambition, the Obama organization goes beyond even what Rove built. The campaign has used its record-breaking fundraising to open more than 700 offices in more than a dozen battleground states, pay several thousand organizers and manage tens of thousands more volunteers.

What effect will this massive effort have at the ballot box?

Don't ask Gallup. On Sunday the polling outfit began offering its likely voter (LV) model (in addition to its registered voter (RV) model). But this year, there's a twist. Gallup is offering two LV models.

Obama's current advantage is slightly less when estimating the preferences of likely voters, which Gallup will begin reporting on a regular basis between now and the election. Gallup is providing two likely voter estimates to take into account different turnout scenarios.

The first likely voter model is based on Gallup's traditional likely voter assumptions, which determine respondents' likelihood to vote based on how they answer questions about their current voting intention and past voting behavior. According to this model, Obama's advantage over McCain is 50% to 46% in Oct. 9-11 tracking data.

The second likely voter estimate is a variation on the traditional model, but is only based on respondents' current voting intention. This model would take into account increased voter registration this year and possibly higher turnout among groups that are traditionally less likely to vote, such as young adults and racial minorities (Gallup will continue to monitor and report on turnout indicators by subgroup between now and the election). According to this second likely voter model, Obama has a 51% to 45% lead over McCain.

So, I guess it's up to us to decide which one is best. This puts us in a tricky spot - because the relationship between extra get out the vote (GOTV) efforts and extra votes on Election Day might be complicated.

In a 2002 article in the Journal of Politics, Charles Bullock, Keith Gaddie and Anders Ferrington investigated "voter falloff" in runoff primaries for the House of Representatives. Their interest was in what factors influence turnout in the second round of voting (which happens in a multicandidate field where nobody wins a majority of the vote). Unsurprisingly, they found that campaign spending is related to voter mobilization: the more dollars a candidate spends between the primary and the runoff, the better turnout the candidate enjoys at the ballot box. However, there's a twist.

They wrote,

The impact is nonlinear. If we assume $100,000 spent between the primary and the runoff, the net impact on the change in voter turnout is just 1.6 points; at $250,000 spent, the impact is an increase of 23.8 points; at $500,000, the impact is a net increase of 30.0 points, all other influences being constant. In a voting system that requires voters to turn out more than once, more campaign spending provides continuous stimulation, and apparently encourages participation, up to a point. With runoff spending averaging less than $100,000, it does little to spur turnout in a number of contests. Spending substantially affects turnout in the 26 runoffs in which more than $150,000 was spent. Diminishing returns from spending begin at about $950,000, and further spending is linked to falling rates of participation. [Emphases Mine]

This means that the relationship between spending and turnout might be a bit more complicated than some pundits have made it out to be. Of course, Bullock et al. looked at congressional runoffs, which are very different from presidential elections. So, we can't draw any inferences about the presidential election from this analysis.

However, this should induce some caution this year. The relationship between Obama's GOTV expenditures and his additional voters might be nonlinear, similar to what Bullock et al. find. That would be a situation in which some law of diminishing marginal returns conditions the relationship.

This makes some sense. If voting is positively related to social connectedness, money would have a decreasing marginal effect. After all, your first "$100k" will bring in people with greater social connections. They're probably paying more attention to political messages and maybe feel a greater social responsibility to vote. You'll get a good response from your GOTV efforts. But after those people come in, your next "$100k" will have to work on pulling people with fewer connections into the system. These people might be paying less attention, which means it will be more expensive to communicate with them, and they might feel a diminished sense of responsibility, which means that it might take more persuasion to get them to actually vote. It would therefore not be surprising that your second "$100k" pulls in fewer voters than your first. How many fewer depends on the precise nature of the law of diminishing marginal returns that governs the process.

I'm not saying that this relationship holds. I'm saying it might. If it does, you can't just look at how much money you're spending, you also have to know a thing or two about this law of diminishing marginal returns. This makes it difficult to estimate the effect of Obama's enhanced GOTV efforts. After all, those efforts are enhanced relative to Kerry's unprecedented efforts. So, that law of diminishing marginal returns, if it exists in this case, might be tamping down on the effect these extra resources have.

The operative word is "might." Contrary to what anybody might tell you, political outsiders can't answer this question - at least not right now. For all the discussion of Obama's GOTV efforts, it's all been about his campaign's inputs - the dollars spent, the organization created, the number of contacts made, and so on. There's no talk of what this is producing in terms of output. How could there be at this point? These contacted voters have not voted yet, so how can we know how efficacious this unprecedented effort will be?

This is where I find myself frustrated by Gallup's approach.

It is polling some 6,000 people per week. If the Obama campaign's unprecedented efforts were producing so many new voters that Gallup's old LV model will be rendered inoperable, we should begin to see some evidence of that in its data. After all, this is October. This would be the point at which Team Obama is really beginning to push these prospective voters into becoming actual voters. If its efforts ultimately prove successful - we should see begin to see that now.

In other words, the correct questions and a proper analysis, combined with a 6,000-person data set, should give us some insight into what kind of output we should expect from all this mobilization input. For instance, what about all those voters who are being excluded by the first LV screen but included by the second? Are they being contacted by the Obama campaign? If so, how frequently? In what way? What effect has this had on them? How has this influenced their thinking relative to voters who are not being contacted? With 6,000 respondents and a good empirical model, it should be possible to provide preliminary answers to these questions. That would give us some sense of which LV model is better.

Instead, Gallup has decided not to arbitrate between its models, leaving the question up to us. But I don't think we can answer it. We don't have the data to make a precise determination, and the relationship between mobilization efforts and new votes is too complicated to spitball.

-Jay Cost