A further 14.9% of homes receive all or almost all calls on mobiles, despite having a landline, meaning that 89 million US adults (nearly two in five) are now cell-only or ‘cell-mostly’.

“The potential for bias due to undercoverage remains a real and growing threat to surveys conducted only on landline telephones,” says the latest report from the National Center for Health Statistics (NCHS), which conducts continuous research on health-related behaviours, as well as landline and cellphone usage.

Many research organisations are beginning to sample cell-only homes alongside landlines, or to use address-based sampling for telephone fieldwork.

The number of cell-only homes has risen steadily from less than 3% when NCHS first started collecting the data in 2003. The latest figure shows a rise of 4.3% percentage points from the same period in 2008, roughly the same rate at which it rose in the twelve months before that.

The proportion of adults who have a landline at home ( 75.4%) is now roughly the same as the proportion who use the internet at home or work (according to estimates of internet usage from Nielsen Online and population estimates from the US Census Bureau).

Among young people the percentage of cell-onlys is even higher, with nearly half ( 48.6%) of 24-29 year-olds living in homes with only cellphones. For 18-24 year-olds and 30-34 year olds, the figure is 37.8% and 37.2% respectively.

The NCHS report highlights demographic differences between cell-only households and the population as a whole, showing that cell-onlys are more likely to be living with unrelated adult roommates, and more likely to be renting.