WASHINGTON - More than one in eight households have cell phones but lack traditional landline telephones, according to a federal study released Monday that tracks the country's growing dependence on wireless phones.
The data, reported twice a year, suggested that the number of households relying solely on cell phones may be growing more slowly than it had in the past. But the researchers said the slowdown might be due to changes in their survey, including altering the order of some questions and some of the wording.
"We don't know how much reflects reality and how much reflects changes in the questionnaire," said Stephen Blumberg, senior scientist at the Centers for Disease Control and Prevention and an author of the report.
The report released Monday showed that for the first half of 2007, 14 percent of households had cell phone service but no landline telephones. That was less than 1 percentage point over the second half of 2006 " not a statistically significant difference.
For the second part of 2006, the increase in those households had been about 2 percent over the previous six-month period.
The growth of families reachable only by cell phone has been of special interest to the telephone industry, providers of 911 emergency services, and public and private polling organizations.
Pollsters typically rely on random calls to households with landline telephones, but some have begun reaching out to cell-phone users, which is more expensive and makes it harder to ensure their samples are truly random.
The federal data showed once again that young, poor, male and Hispanic people are likelier to have only wireless telephone service.
Nearly one in five Hispanic adults " 18 percent " have cell phones but no landline phones, the survey showed. That was up from 15 percent in the last half of 2006.
In addition for the first half of 2007,
_11 percent of white adults and 14 percent of black adults had only cell phone service.
_Roughly three in 10 people age 18 to 29 had only wireless telephones " more than double the portion of those age 30 and older who rely only on cell phones.
_14 percent of males and 12 percent of females only had cell phone service.
_About one in five poor people have only cell phones, about double the percentage for those who are not poor.
_59 percent of households have landlines and cell phones, and 24 percent have only landlines.
The National Health Interview Survey, conducted by the CDC, involved in-person interviews with people in 15,996 households conducted from January through June of this year.
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