Around a quarter (24.9%) of Americans no longer have home telephones, according to a report published by the Center for Disease Control (CDC), which warns that the potential for bias due to undercoverage remains a 'real and growing threat' to surveys.
For many years, CDC's National Health Interview Survey (NHIS) has asked survey respondents to provide residential telephone numbers, and in 2003 it added questions to determine whether a family has a landline telephone.
Stats released yesterday were collected between January and June 2010 from 17,619 households that included at least one adult or child. These households included 33,780 adults aged 18 years and over and 12,234 children under the age of 18.
In the first 6 months of 2010, results indicated that more than one out of every four American homes (26.6%) did not have a landline, but had at least one wireless telephone - an increase of 2.1 percentage points since the second half of 2009.
In terms of demographics, adults working at a job or business (20.8%) and adults going to school (23.5%) were more likely to be living in 'wireless-mostly' households than were adults keeping house (14.5%) or with another employment status such as retired or unemployed (11.5%).
Meanwhile, adults living in poverty (11.0%) and adults living near poverty (12.6%) were less likely than higher income adults (20.8%) to be living in wireless-mostly households.
Nearly one of every six (15.9%) of American homes with a landline received all or almost all calls on wireless telephones.
As the NHIS report notes, researchers are concerned that some people living in households with landlines cannot be reached on those landlines because they rely on wireless telephones for all or almost all of their calls.
This is born out by the results of a study conducted by the Pew Research Center in October, which demonstrated the 'increasing likelihood that public opinion polls conducted only by landline telephone will be biased.'
At the time, Pew also found that support for Republican candidates was significantly higher in samples based only on landlines, than in ones including cellphone interviews.
Web sites: www.cdc.gov/nchs and www.pewresearch.org .