According to the Census Bureau’s 2007 American Community Survey estimates, 95% of households (106.3 million households) in the United States have telephone service. To represent these telephone households in a sample is a challenge for several reasons: households without landline telephone service, unlisted by choice, and unlisted by circumstance (mobility).

The National Center for Health Statistics reported that in 2008, roughly 20% of all households had only wireless or cell phone service and only 76% of households could be reached on a landline telephone. Approximately 30% of the landline telephone households in the U.S. have unlisted numbers. Each year, about 20% of American households move, so that 12-15% of the residential numbers in a typical directory are disconnected over the life cycle of the directory.

Samples drawn entirely from directories, and “plus-one” techniques based on directory seed numbers, often significantly under-represent unlisted households. To address these representation issues, SSI developed a variety of random digit (RDD) methodologies. (Refer to the SSI Wireless Methodology-US information sheet for more detail on supplementing landline RDD samples with Wireless/Mobile RDD sample.) SSI’s random digit landline methodology is unsurpassed in efficiency. You’ll experience fewer dialings, faster completion, and improved interviewer morale.