Political polling in the U.S. is undergoing significant changes because of the growing popularity of cell phones and the diminishing number of Americans with traditional land lines, says Brian F. Schaffner, a political scientist at the University of Massachusetts Amherst.
He says the shift to cell phones means that traditional public opinion polls based on calling large random samples of the population that have been familiar since the 1950s really dont exist anymore. "Polling is getting more difficult," Schaffner says. "No matter how you do it, you cant get a truly random sample."
Adjusting polling methods to reflect these new demographic realities requires understanding what those changes are and which groups of people are affected, he says. For example, Schaffner estimates that between 35 and 40 percent of Americans are very difficult or impossible to reach on those traditional land line telephones. He says, "People who can be reached by land lines tend to be older, have families, and are more connected to their communities."
The other key element is the growing number of people, including many young people, who use only cell phones. In a recent study Shaffner conducted with a colleague, Stephen Ansolabehere of Harvard, they found, "One in five households relies exclusively on cell phones for telecommunications. That fact has created coverage problems for phone surveys, and the demographics of this population--younger, mobile, less socially connected--may create biases in political surveys limited to random dialing samples."
Schaffner says many polling organizations now adjust for these changes by including cell phones users, but not all. In fact some well-known pollsters, such as Rasmussen and Survey USA, dont include cell phone users and these companies produce many of the statewide polls that political onlookers are watching during this election season. According to Schaffner, "These surveys run the risk of being biased in favor of Republicans because they are more likely to exclude groups, like younger adults, who vote more Democratic."
Schaffner notes that while polls attempt to use statistical techniques to adjust for the fact that they are missing those with only cell phones, these adjustments are become less effective with time, forcing pollsters to rethink their approach to polling. "The increasing numbers of cell-phone-only Americans is making telephone polling much more complicated and costly, as a result pollsters are looking seriously at new approaches to polling like Internet surveys," he says.
Explore further: Presidential primary 2008 polls: What went wrong