The impact of cell phones on public health surveillance

Random-digit-dial telephone sampling of households with landline telephones has been a popular tool for conducting surveys of the population in the United States of America (USA) in the past several decades. These surveys have provided a cost-efficient strategy for conducting population-based surveys, have sound sampling characteristics and have benefited from high coverage of landline telephones reaching more than 90% of American households from 1970 to 2004.1 However, in the past 10 years the utility of random-digit-dial telephone surveys is being questioned due to another trend in telephone usage – the increased popularity of cell (mobile or portable) phones. More and more telephone users are switching from landline telephones to cell phones, reducing the number of households with landline telephones and, therefore, lowering the coverage of traditional random-digit-dial surveys that don’t include cell phone numbers.