Yesterday, the National
Center for Health
Statistics (NCHS) released its latest estimates of the number of Americans
living in households without landline telephones, as well as a statistic
closely watched by pollsters: During the first six months of 2006, "approximately
10.5 percent of households do not have a traditional landline telephone, but do
have at least one wireless telephone."
Pollsters have been watching the growth in "cell phone only" households
because cell phones are largely out of reach of the traditional random digit
dial sampling methods used in most conventional telephone surveys. As such, the continuing upward tend in such
households illustrated by the NCHS surveys (which involve massive monthly in-person
samples of Americans), should be of great interest to anyone who follows public
Although I have written about these issues previously (here,
the best analysis of how this trend has affected the accuracy of public polling
has been done by the Pew Research Center.
Last year, in partnership with the
Associated Press and America Online, they conducted parallel surveys: One
using conventional telephone sampling and another that interviewed a random
sample of 750 mobile phone users over their mobile phones. The study produced a report by the Pew Research
Center (available in
or PDF format)
reached the following conclusions:
[Cell only Americans] are younger, less affluent,
less likely to be married or to own their home, and more liberal on many
Yet despite these differences, the
absence of this group from traditional telephone surveys has only a minimal
impact on the results. Specifically, the study shows that including cell-only
respondents with those interviewed from a standard landline sample, and weighting
the resulting combined sample to the full U.S. public demographically, changes
the overall results of the poll by no more than one percentage point on any of
nine key political questions included in the study.
Of course, given the trend reported by NCHS, the cell-phone only adult population appears to be a moving target. It has more than doubled in the last two
years, and the trend shows no signs of slowing.
How big a problem will cell-phone only households be in 2008? Will their absence from traditional phone surveys begin to impact results? Will pollsters begin to routinely incorporate more expensive cell phone samples into their surveys? Time will tell.