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Objectives: Since 1994 the National Immunization Survey (NIS) has monitored progress toward the Healthy People 2000 and 2010 vaccination goals. The NIS collects data in two phases: first, a random-digit-dialing (RDD) telephone survey to identify households with children 19-35 months old and, second, a mail survey to vaccination providers to obtain vaccination histories used to estimate vaccination coverage rates. This report reviews the methodologies used in the 1994-2002 NIS to obtain official estimates of vaccination coverage and describes the methodology used for the first three topical modules of the NIS., Methods: From 1994 to 1997 the NIS used a variation of a two-phase estimator to compensate for missing provider-reported vaccination histories. Between 1998 and 2001 a weighting-class estimator was used. In 2002 and thereafter the weighting-class approach was refined to account for households that do not have telephones and for unvaccinated children. To collect data on immunization-related topics, the NIS sample was randomized among three topical modules: health insurance and ability to pay for vaccinations (HIM); parental knowledge and experiences about vaccinations (PKM); and daycare attendance, breastfeeding practices, and participation in the Special Supplemental Nutrition Program for Women, Infants, and Children (DCM)., Results: In 2001 among children with completed RDD interviews, 0.3 percent were entirely unvaccinated. Together, the new nontelephone adjustment and the refinement for unvaccinated children yielded revised estimates that were within 1.5 percentage points of the original estimates obtained using the 1998-2001 methodology. Over the six quarters during which the first three topical modules were fielded (from mid-2001 through 2002), 21,163 children were randomized to the HIM, 3576 to the PKM, and 3511 to the DCM.

Objectives: The National Immunization Survey (NIS) uses two phases of data collection to obtain vaccination information from a sample of young children: a random-digit-dialing (RDD) survey for identifying households with children 19-35 months of age, followed by a mail survey for obtaining provider-reported vaccination histories about these children. Provider-reported vaccination histories are used to estimate vaccination coverage rates. In 1998, provider-reported vaccination histories were not obtained for 32.9% of children with a completed RDD interview. This report describes the statistical methods adopted in 1998 to reduce the bias in vaccination coverage estimates that could result from "vaccination history nonresponse," that is, differences between children for whom provider data was obtained and those for whom it was not obtained., Methods: In the methods adopted in 1998, children with completed NIS RDD interviews are grouped into adjustment cells defined by their propensity to have adequate provider data. Sampling weights of children with adequate provider data are divided by the cell-specific weighted response rate to allow these children to represent all children in the cell., Results: Using an "optimal" number of cells, the overall extent of bias reduction was 0.5%, suggesting that provider nonresponse bias was small. Authoritative literature suggests using five cells. No statistically significant differences were observed in vaccination coverage estimates when comparing estimates based on the "optimal" number of cells with five cells. Thus, five adjustment cells are used to reduce provider nonresponse bias in the NIS vaccination coverage estimates. No substantively important differences were observed between estimates based on the methodology used prior to 1998 and the methodology adopted in 1998.