Noncoverage Errors in Travel Surveys Due to Mobile Phone–Only Households

Abstract

National and regional household travel surveys have conventionally sampled landline telephone households through list-assisted random digit dialing. However, recent increases in “mobile phone-only” households result in either noncoverage or undercoverage of a growing segment of the population. This result could cause a substantial bias in the representativeness of travel behavior toward the target population. To cover mobile phone-only households, an address-based sampling method is of interest. This study explores whether the characteristics and travel behavior of mobile phone-only households differ from those of households with landline telephones. In addition, this study quantifies the extent of noncoverage errors in the surveys in respondents’ travel behavior. Along with census data, the mobile phone-only sample (N = 2,988) was compared with the landline telephone sample (N = 7,774) drawn from the 2008 National Capital Region Household Travel Survey. Results show that the mobile phone-only sample consisted of relatively more single-person households; younger individuals; and Blacks, Asians, and Hispanics, who were generally identified as hard-to-reach groups. Statistical models were estimated to examine differences in travel behavior and suggested that the mobile phone-only households made more transit (41%) and walking (29%) trips. This study shows that the inclusion of the mobile phone-only households can reduce the noncoverage errors, especially for alternative modes. The implications for travel survey methods are discussed.