Pollster.com

Articles and Analysis

 

"Likely Voters" and 2008

Topics: 2008 , ABC/Washington Post , Barack Obama , Gallup , John McCain , Likely Voters , Pollsters , USA Today

TNR's Noam Scheiber wonders whether national polls that report on the preferences of "registered voters" might "understate the support of the candidate with the enthusiasm on his side--Obama in this case" as compared to state level surveys that are typically reporting on the preferences of "likely voters."

He sees a some suggestive evidence in the apparent enthusiasm gap identified in the ABC/Post poll (as per today Post article):

But [McCain] starts that campaign with several deficits, including an enthusiasm gap. A majority of voters, 55 percent, said they are enthusiastic about Obama's candidacy, while 42 percent said the same for McCain. Three times as many said they are "very enthusiastic" about Obama as said so about McCain.

Even among McCain and Obama supporters, there is a clear difference in interest.

Ninety-one percent of Obama's supporters are enthusiastic about his candidacy, including 54 percent who are very enthusiastic. Fewer of McCain's backers are as ardent: 73 percent are enthusiastic about his run, but just 17 percent are very much so. There appears to be some leftover animosity toward him on the right. Overall, 13 percent of conservatives are very enthusiastic about McCain, compared with nearly half of liberals who feel as strongly about Obama.

The theory that Obama's enthusiasm advantage may translate into a a turnout edge is intriguing but difficult to prove with the data we have available right now. The main reason is that this far from an election, the process of identifying true "likely voters" is a sketchy exercise at best.

True, media pollsters have spent decades developing likely voter "models" to identify the true electorate, but most of that research identifies characteristics that are proven to predict turnout a few weeks before the election (or background, see my blogging on this topic from October 2004). The most elaborate approaches, like the classic Gallup likely voter model, use self-reported registration, intent to vote, past vote history, interest in the campaign and knowledge of voting procedures to score each respondents probability of voting. They then separate likely voters from less likely (or weight the most likely more heavily than the least likely) based on their assumptions about the level of turnout.

The basis for these models are validation studies that measure how well these variables predict turnout, and almost all were conducted in the final weeks of the campaign, not in June. And we have other evidence -- most notably a 2004 POQ article by Robert Erikson and his colleagues -- showing that the Gallup model may introduce too much volatility into the survey results before October. As a result, most national pollsters report on registered voters until the fall.

With those warnings in mind, we do have Gallup data for both registered and "likely" voters (using their traditional model) for the seven surveys they conducted so far during 2008 in partnership with USA Today. I copied those into the table below. They show a very slight pattern supporting Scheiber's theory. Obama did a point or two better among likely voters (but no better) on six of the seven surveys. On average across all the surveys, however, this "effect works out to four tenths of a percentage point.

2008-06-17_GallupLV.png

Back in 2004 we typically saw the reverse pattern. Bush did slightly better than Kerry with "likely voters" using the Gallup style model, than with all registered voters.

Unfortunately, we know less little about the "likely voter" models used by most state level polls, as pollsters tend to divulge few details about their methods. However, those that have shared details typically use relatively simple screens for registered voters who say they are likely to vote in November. Since virtually all self-described registered voters say they are likely to vote, these "likely voter" screens are functionally not much different from the registered voter results we are seeing on national surveys (this conclusion is not warranted for the handful of state level polls using list samples to select those with past voting history, but that is another topic altogether).

 

Comments
hobetoo:

On the possible effect of the enthusiasm gap on the representativeness of polls using registered vs. likely voter screens, I would suggest the following point for consideration.

If candidate A is generating a lot more enthusiasm among his supporters than Candidate B is among his own supporters, then it also seems likely that candidate A's supporters would be more likely to participate in polls. Rather than being underrepresented, then, Candidate A's supporters would perhaps be more likely to be overrepresented than Candidate B's. (I'm thinking of John Brehm's argument that participation in polls is akin to participating in politics, and so the same factors that predispose people to vote are likely to predispose them to consent to an interview.)

____________________



Post a comment




Please be patient while your comment posts - sometimes it takes a minute or two. To check your comment, please wait 60 seconds and click your browser's refresh button. Note that comments with three or more hyperlinks will be held for approval.

MAP - US, AL, AK, AZ, AR, CA, CO, CT, DE, FL, GA, HI, ID, IL, IN, IA, KS, KY, LA, ME, MD, MA, MI, MN, MS, MO, MT, NE, NV, NH, NJ, NM, NY, NC, ND, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VT, VA, WA, WV, WI, WY, PR