• by Mark Walsh  @markfwal, August 13, 2009

Underscoring the growing number of so-called cord cutters, Scarborough Research said it will start including cell phone-only users in samples for its local market studies. The consumer and media research firm will begin field work for studies reflecting mobile-only participants this summer, with data being released in spring 2010.

"Cell phones have become ubiquitous. We recognize the need to ensure those consumers who use their cell phone as their primary phone are included in our survey," commented Steve Seraita, executive vice president of sales at Scarborough, in a statement. "

Nearly one-quarter (24%) of U.S. households have switched from traditional wireline service to mobile-only, according to second-quarter figures from mobile research and consulting firm Chetan Sharma. That's up from 18% a year ago.

A separate study by the National Health Interview Survey (NHIS) estimated that 20.2% of U.S. homes had only wireless phones at the end of 2008. A Nielsen study report last year found cord cutters tend to have lower incomes and be part of households with just one or two residents.

The bigger the portion of the population that gives up landlines in favor of mobile phones, the bigger the challenge it poses for consumer research companies to reach people to assemble surveys reflecting a representative sample of the population.

Scarborough will combine the cell phone-only sample with its wireline-based survey data and roll out the new data for studies in 10 local markets including Austin, Texas, Oklahoma City, Columbus, OH, Pittsburgh and Denver. Additional markets will be added in the coming months.

A joint venture between Arbitron and The Nielsen Company, Scarborough measures the demographics, shopping patterns and media habits of Americans locally, regionally and nationally.