Yesterday, the National Center for Health Statistics (NCHS) today released its biannual update on the still growing number of Americans living in households without a landline telephone:
Preliminary results from the January–June 2007 National Health Interview Survey (NHIS) indicate that more than one out of every eight American homes (13.6%) had only wireless telephones during the first half of 2007.
The NCHS is an invaluable source of data on the growing mobile-phone only population because it conducts more than 13,000 in-person interviews every six months that reach all Americans, regardless of their telephone service (or the lack thereof). The Centers for Disease Control (of which NCHS is a part) is concerned about the growth of "cell phone only" households because of the massive ongoing health "surveillance" studies it conducts via telephone.
When we last checked in with the NCHS data, the rate of growth appeared to be increasing, as evident in the upturn in the trend in the chart above from July 2005 through December 2006. That rate of growth appears to have slowed on the most recent release, but the NCHS report explains that the change may be due to a changes in the NCHS questionnaire:
The observed increase in the percentage of adults living in wireless-only households from the last 6 months of 2006 to the first 6 months of 2007 was not statistically significant. Other observed increases over time in the percentage of adults living in wireless-only households were statistically significant. These results suggest a possible recent decline in the rate of increase. However, questionnaire changes in 2007 could have contributed to the observed decline. Therefore, conclusions about trends cannot be made until data from the last 6 months of 2007 are released in May 2008.
The full NCHS report has details on those questionnaire changes.
AP also published concise summary yesterday of the findings from NCHS Report. For more information on the impact of the growing "cell phone only" population on political surveys, see my two-part series earlier this year.