The term telephone penetration refers to the number of households in a given survey area with one or more telephones. Traditionally, this has meant one or more landline or wired telephones, not including cell phones. A major challenge for drawing proper survey samples is ensuring that the sample represents a very high proportion of the population of interest. Traditionally, bias as a result of undercoverage in telephone surveys was credited to households without phones. As time has gone on, the rate of households without phones has been declining, leading to a decline of said bias. In its infancy, telephone interviewing was used only as a method of support for other interviewing techniques, such as face-to-face interviewing. However, by the 1970s the penetration of telephones in ...