The rapid growth in cell-phone-only households is pressuring public opinion researchers to adapt their surveying methods, which are based heavily on telephone interviews of people with traditional landline phones.
The number of households using only a mobile phone doubled in less than two years, with the rate rising faster among certain groups, researchers found. "The polling community needs to come up with a strategy sooner rather than later," said Stephen Blumberg, a senior scientist at the Centers for Disease Control and Prevention.
Blumberg presented his survey findings about cell phone use at the annual meeting this weekend of the American Association for Public Opinion Research.
Slightly more than 6 percent of households do not have a traditional landline phone, but do have at least one wireless phone. About 5.5 percent of adults have only a mobile phone, research found.
Those findings come from the CDC's National Health Interview Survey. Researchers interviewed 37,476 adults face to face during the second half of 2004. The mobile phone data was compared with a similar survey conducted in the first half of 2003.
For adults in school, the rate of mobile phone use tripled in that time. Also, the number of people using only mobile phones was growing faster among several groups — including young adults, those people living with unrelated roommates and those people living alone.
Public opinion research, such as government surveys, market research and political polls, faces obstacles in dealing with the cell-phone-only crowd. They include:
- legal restrictions on use of automated dialing equipment
- difficulty contacting a very mobile group of people
- cell phone owners' concerns about using up costly minutes in their calling plans
- how to statistically blend cell phone results into traditional polls.
During the 2004 election, concerns arose about polls that missed young adults who were reachable only by cell phone. But research suggested the impact was limited because this was a relatively small group and their attitudes were not sharply different from people who could be contacted on traditional phones.
But the trend indicated in the CDC survey suggested that effects on polling are coming soon.
Arbitron, a company that tracks radio ratings, is experimenting with surveys that contact those on cell phones. The company plans to incorporate those findings into their tracking of radio habits.
Clyde Tucker, a researcher at the Labor Department's Bureau of Labor Statistics who tracks cell phone use, found that many adults who have traditional phones use their cell phones for much of their communication. That could pose an additional problem for phone surveys.
"We've identified the problems and the questions that need to be answered," said the CDC's Blumberg, "We've got some people working on the answers to those questions. But there's more work to be done."
