Since 1994, the Centers for Disease Control and Prevention has funded the National Immunization Survey (NIS), a large telephone survey used to estimate vaccination coverage of U.S. children aged 19–35 months. The NIS is a two-phase survey that obtains vaccination receipt information from a random-digit-dialed survey, designed to identify households with eligible children, followed by a provider record check, which obtains provider-reported vaccination histories for eligible children. In 2006, the survey was expanded for the first time to include a national sample of adolescents aged 13–17 years, called the NIS-Teen. This article summarizes the methodology used in the NIS-Teen. In 2008, the NIS-Teen was expanded to collect state-specific and national-level data to determine vaccination coverage estimates. This survey provides valuable information to guide immunization programs for adolescents.

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Random-digit-dial telephone surveys are experiencing both declining response rates and increasing under-coverage due to the prevalence of households that substitute a wireless telephone for their residential landline telephone. These changes increase the potential for bias in survey estimates and heighten the need for survey researchers to evaluate the sources and magnitudes of potential bias. We apply a Monte Carlo simulation-based approach to assess bias in the NIS, a land-line telephone survey of 19-35 month-old children used to obtain national vaccination coverage estimates. We develop a model describing the survey stages at which component nonsampling error may be introduced due to nonresponse and under-coverage. We use that model and components of error estimated in special studies to quantify the extent to which noncoverage and nonresponse may bias the vaccination coverage estimates obtained from the NIS and present a distribution of the total survey error. Results indicated that the total error followed a normal distribution with mean of 1.72 per cent(95 per cent CI: 1.71, 1.74 per cent) and final adjusted survey weights corrected for this error. Although small, the largest contributor to error in terms of magnitude was nonresponse of immunization providers. The total error was most sensitive to declines in coverage due to cell phone only households. These results indicate that, while response rates and coverage may be declining, total survey error is quite small. Since response rates have historically been used to proxy for total survey error, the finding that these rates do not accurately reflect bias is important for evaluation of survey data. Published in 2011 by John Wiley & Sons, Ltd.

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