In recent dinnertable conversations about the election, I've faced a lot of questions about the reliability of presidential polling and the so-called "cellphone effect." There is a widespread perception that major pollsters don't include cellphone numbers in their surveys and, as such, exclude the growing number of people -- particularly young folks, a key Democratic demographic -- who don't have land lines. Thanks to Michael Moore's emphasis on this issue during the 2004 cycle, I too believed that all mobile users were still shut out of the polling universe. But it turns out that more and more pollsters are integrating cellphone numbers into their databases. From Pollster.com's Mark Blumenthal:
Over the last four years, survey researchers have been developing techniques for interviewing respondents on their cell phone, and over the last few months, many of the well known national media surveys have been including samples of voters contacted on their cell phones in their national samples or conducting side-by-side tests. These include the Pew Research Center, Gallup (both the Gallup Daily and USA Today/Gallup surveys), CBS/New York Times, Time/SRBI and most recently NBC/Wall Street Journal, ABC/Washington Post and the new AP/GfK poll.
FiveThirtyEight's Nate Silver added a few others to this list: Ann Selzer and California's Field Poll. Then, comparing these pollsters' results to other surveys, he estimated that "including a cellphone sample improves Obama's numbers by 2.8 points." Silver then explained the potential effect on his electoral regression analysis if every pollster integrated mobile users:
A difference of 2-3 points may not be a big deal in certain survey applications such as market research, but in polling a tight presidential race it makes a big difference. If I re-run today's numbers but add 2.2 points to Obama's margin in each non-cellphone poll, his win percentage shoots up from 71.5 percent to 78.5 percent, and he goes from 303.1 electoral votes to 318.5.
In short, there appears to be statistical support for concerns about the "cellphone effect." Some pollsters are doing their part to address the issue. But there are plenty more who could follow suit.
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