Cellphones taking a toll on health surveys, researchers say

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 the country's epidemiologists.

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

In public health, pretty much everything depends on good data. Researchers and policy makers 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 a decade ago? Is the recession limiting 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 with 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, 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 show that people who have only cellphones are different from people without them or who use them only occasionally.

The risk-factor surveys 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.

Federal law makes it illegal to call cellphones using automatic dialers, which are standard tools for survey and polling firms. Furthermore, a huge fraction of "owners" of cellphone numbers are minors ineligible for the health surveys. And some cellphone users are reluctant to talk at length because they have to pay by the minute for incoming as well as outgoing calls.

Consequently, it takes roughly nine calls to working cellphone numbers to get one completed survey, compared with five calls to working land-line numbers, said Scott Keeter, a polling expert at the Pew Research Center for the People & the Press, an independent opinion research group. Further, an interview conducted with someone who uses a cellphone costs 2.5 times more than an interview with someone on a conventional phone. In addition to the higher labor costs to obtain a completed survey, most polling organizations now reimburse cellphone users for their minutes, either in cash or through credits to online merchants such as Amazon.com.

People's willingness to answer questions has also been affected by the barrage of calls, many unsolicited, they get every day. The response rate in public opinion polls has fallen from about 60 percent two decades ago to 25 percent now, according to Keeter.