Cellphones' Growth Does a Number on Health Research

By David Brown
Washington Post Staff Writer
Monday, January 12, 2009

In our information-crazy, never-out-of-touch world, it's becoming harder and harder to find out who we are and what we do.

That's the ironic truth facing epidemiologists around the country.

The popularity of cellular telephones, an increasingly mobile population, rising expenses, flat budgets and new insights into ways people can answer a question differently depending on how it's asked -- all are conspiring to make health surveys more difficult.

In public health, pretty much everything depends on good data. Researchers and policymakers can't identify a problem, figure out whether it's serious and devise a strategy to fight it without first being able to count it. "If you can't measure something, you won't be able to change it" is an oft-heard aphorism.

How big a problem is obesity? Are restrictions on smoking changing people's habits? Is autism more prevalent than it was a decade ago? Is the recession affecting people's access to health insurance?

All are questions of national importance -- and none can be answered without unbiased surveys of a representative sample of the population.

Cellular telephones are perhaps the biggest threat to survey data that epidemiologists have confronted in years.

The National Center for Health Statistics reported that in the first half of last year, 16 percent of American adults lived in households that have only cellphones. This was up from 7 percent three years earlier, and rising rapidly.

The federal government's main tool for measuring the health habits of Americans, the Behavioral Risk Factor Surveillance System (BRFSS), uses the telephone to interview a nationwide sample of adults (470,000 this year). Historically, interviewers called only conventional telephones, as all but the 2 to 3 percent of households with no phones at all could be reached through them. But that's not remotely true anymore.

Surveyors, however, cannot just extrapolate from the land-line respondents. That's because studies have shown that people who have only cellphones are different from people who don't have them or use them only occasionally.

Young people, men and Hispanics are all more likely than the "average" American to have cellphones only. But those demographic factors don't explain everything. Even after they are taken into account by statistical means, cellphone-only users are different.

The BRFSS surveyors this year will include cellphone numbers in every state, with a goal of having 10 percent of the interviews done that way. But it's easier said than done.

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