Coverage bias in traditional telephone surveys of low-income and young adults

The proportion of adults with only wireless telephones is growing rapidly. Using 2006 data from the National Center for Health Statistics' National Health Interview Survey, this article is among the first to reveal that noncoverage of this population can result in nonnegligible bias for traditional random-digit-dial landline telephone surveys that do not call wireless telephone numbers. In 2006 in the United States, 17 percent of low-income adults with household income below 200 percent of the federal poverty thresholds, 25 percent of young adults aged 18-29 years, and 32 percent of low-income young adults lived in households with only wireless telephones. Within each of these three subgroups, we compared wireless-only adults and adults with landline telephones on demographic characteristics and 13 key indicators of health status, health behaviors, health care service use, and health care access. Even after statistical adjustments that account for demographic differences between adults living in households with and without landlines, telephone surveys of landlines will underestimate the prevalence of health behaviors, such as binge drinking, smoking, and HIV testing. Obesity may be overestimated and physical activity may be underestimated for low-income young adults. No significant bias is predicted for other measures of health status and health insurance coverage. Sample weighting procedures that incorporate adjustments for multiple demographic characteristics are necessary to help attenuate coverage bias in traditional telephone surveys, but may not be sufficient for behavioral risk factor surveys of low-income and young adults.