Preliminary results from the National Health Interview Survey (NHIS), conducted between January and June 2011, indicate that the percentage of American households with wireless-only telephone access has risen to 32%. This is a 1.9 percentage point increase from the second half of 2010.

The percentage of wireless-only households was found to be higher still among 25-29 year olds ( 58.1%), home-renters ( 52.5%), and Hispanic adults ( 40.8%).

Scott Keeter, director of survey research at the Pew Research Centre and president of the AAPOR, said: “For market researchers, the absence of these groups, especially young people, from landline samples is a serious challenge given the interest they have in studying consumer attitudes and behaviour among what are the prime product-purchasing age groups.”

AAPOR guidelines were last updated in 2010, when the wireless-only proportion passed 1 in 4 American households. At the time, AAPOR warned that researchers risked unrepresentative results when studying the full US population if they didn’t make efforts to include cell-only homes in their sample designs.

Keeter said today: “I don’t think anything has really changed to any great degree from the situation in 2010, apart from that the size of the [cell-only] population is getting larger.

“If we’re talking about estimating behaviours or characteristics of a population that requires a great deal of precision, then you probably can’t tolerate the degree of bias that we already have [in landline samples].”