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Objectives: To examine the effect on estimated levels of health conditions produced from large-scale surveys, when either list-wise respondent deletion or standard demographic item-level imputation is employed. To assess the degree to which further bias reduction results from the inclusion of correlated ancillary variables in the item imputation process., Design: Large cross-sectional (US level) household survey., Participants: 218 726 US adults (18 years and older) in the 2006 Behavioral Risk Factor Surveillance System Survey. This survey is the largest US telephone survey conducted by the Centers for Disease Control and Prevention., Primary and Secondary Outcome Measures: Estimated rates of severe depression among US adults., Results: The use of list-wise respondent deletion and/or demographic imputation results in the underestimation of severe depression among adults in the USA. List-wise deletion produces underestimates of 9% (8.7% vs 9.5%). Demographic imputation produces underestimates of 7% (8.9% vs 9.5%). Both of these differences are significant at the 0.05 level., Conclusion: The use of list-wise deletion and/or demographic-only imputation may produce significant distortion in estimating national levels of certain health conditions.

To meet challenges arising from increasing rates of noncoverage in US landline-based telephone samples due to cell-phone-only households, the Behavioral Risk Factor Surveillance System (BRFSS) expanded a traditional landline-based random digit dialing survey to a dual-frame survey of landline and cell phone numbers. In 2008, a survey of adults with cell phones only was conducted in parallel with an ongoing landline-based health survey in 18 states. The authors used the optimal approach to allocate samples into landline and cell-phone-only strata and used a new approach to weighting state-level landline and cell phone samples. They developed logistic models for each of 16 health indicators to examine whether exclusion of adults with cell phones only affected estimates after adjustment for demographic characteristics. The extents of the potential biases in landline telephone surveys that exclude cell phones were estimated. Biases resulting from exclusion of adults with cell phones only from the landline-based survey were found for 9 out of the 16 health indicators. Because landline noncoverage rates for adults with cell phones only continue to increase, these biases are likely to increase. Use of a dual-frame survey of landline and cell phone numbers assisted the BRFSS efforts in obtaining valid, reliable, and representative data., (Published by Oxford University Press on behalf of the Johns Hopkins Bloomberg School of Public Health 2011.)

Use of random-digit dialing (RDD) for conducting health surveys is increasingly problematic because of declining participation rates and eroding frame coverage. Alternative survey modes and sampling frames may improve response rates and increase the validity of survey estimates. In a 2005 pilot study conducted in six states as part of the Behavioral Risk Factor Surveillance System, the authors administered a mail survey to selected household members sampled from addresses in a US Postal Service database. The authors compared estimates based on data from the completed mail surveys (n = 3,010) with those from the Behavioral Risk Factor Surveillance System telephone surveys (n = 18,780). The mail survey data appeared reasonably complete, and estimates based on data from the two survey modes were largely equivalent. Differences found, such as differences in the estimated prevalences of binge drinking (mail = 20.3%, telephone = 13.1%) or behaviors linked to human immunodeficiency virus transmission (mail = 7.1%, telephone = 4.2%), were consistent with previous research showing that, for questions about sensitive behaviors, self-administered surveys generally produce higher estimates than interviewer-administered surveys. The mail survey also provided access to cell-phone-only households and households without telephones, which cannot be reached by means of standard RDD surveys.

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.

In complex probability sample surveys, numerous adjustments are customarily made to the survey weights to reduce potential bias in survey estimates. These adjustments include sampling design (SD) weight adjustments, which account for features of the sampling plan, and non-sampling design (NSD) weight adjustments, which account for non-sampling errors and other effects. Variance estimates prepared from complex survey data customarily account for SD weight adjustments, but rarely account for all NSD weight adjustments. As a result, variance estimates may be biased and standard confidence intervals may not achieve their nominal coverage levels. We describe the implementation of the bootstrap method to account for the SD and NSD weight adjustments for complex survey data. Using data from the National Immunization Survey (NIS), we illustrate the use of the bootstrap (i). for evaluating the use of standard confidence intervals that use Taylor series approximations to variance estimators that do not account for NSD weight adjustments, (ii). for obtaining confidence intervals for ranks estimated from weighted survey data, and (iii). for evaluating the predictive power of logistic regressions using receiver operating characteristic curve analyses that account for the SD and NSD adjustments made to the survey weights., (Copyright 2003 John Wiley & Sons, Ltd.)

Telephone surveys are widely used in the U.S.A. for the study of health-related topics. They are subject to 'coverage bias' because they cannot sample households that do not have telephones. Although only around 5 per cent of households do not have a telephone, rates of telephone coverage show substantial variation by geography, demographic factors and socio-economic factors. In particular, lack of telephone service is more common among households that contain ethnic and racial minorities or that have lower socio-economic status with fewer opportunities for access to medical care and poorer health outcomes. Thus, failure to adequately account for households without telephones in health surveys may yield estimates of health outcomes that are misleading, particularly in states with at least moderate telephone non-coverage. The dynamic nature of the population of households without telephones offers a way of accounting for such households in telephone surveys. At any given time the population of telephone households includes households that have had a break or interruption in telephone service. Empirical results strongly suggest that these households are very similar to households that have never had telephone service. Thus, sampled households that report having had an interruption in telephone service may be used also to represent the portion of the population that has never had telephone service. This strategy can lead to a reduction in non-coverage bias in random-digit-dialling surveys. This paper presents two methods of adjusting for non-coverage of non-telephone households. The effectiveness of these methods is examined using data from the National Health Interview Survey. The interruption-in-telephone-service methods reduce non-coverage bias and can also result in a lower mean squared error. The application of the interruption-in-telephone-service methods to the National Immunization Survey is also discussed. This survey produces estimates for the 50 states and 28 urban areas. The interruption-in-telephone-service estimates tend be slightly lower than estimates resulting from poststratification and from another non-coverage adjustment method. The results suggest that the reduction in bias is greatest for variables that are highly correlated with the presence or absence of telephone service.

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.

Abstract: The National Immunization Survey (NIS) is a large federally funded survey designed to estimate vaccination coverage rates for children residing in the United States aged 19 to 35 months. In 1999, over 8 million telephone call attempts were made to obtain provider-reported vaccination histories on 22,521 children in the age range of interest.

Objective: To estimate the vaccination coverage levels of children living in rural areas and identify statistically significant differences in coverage between children living in rural areas and their suburban and urban counterparts., Methods: Children aged 19 to 35 months participating in the 1999 National Immunization Survey (NIS) were included in the study. Children were classified as living in a rural, urban, or suburban area based on their telephone exchange (area code plus the first three digits of the telephone number). Statistically significant differences in vaccination coverage levels between the rural population and their urban counterparts were determined for individual vaccines and vaccine series., Results: Overall, 18% of the children included in the 1999 NIS lived in a rural area, 46% lived in a suburban area, and 36% lived in an urban area. The characteristics of the rural population were: 72% were white, non-Hispanic; 24% were below the poverty level; 16% had a mother with <12 years of education; and 30% received vaccinations from a public provider. Eighty percent of rural children, 79% of suburban children, and 77% of urban children completed the 4:3:1:3 series. The rural population had statistically significantly lower (p<0.01) varicella coverage levels than their suburban and urban counterparts., Conclusion: Results of this study suggest that children living in rural areas are just as likely to receive the basic 4:3:1:3 vaccination series as their suburban and urban counterparts. Uptake of the varicella vaccine appears to be slower in rural areas than urban areas. Further studies are recommended to identify the risk factors for not receiving the varicella vaccine in rural areas.

The National Immunization Survey (NIS) was designed to measure vaccination coverage estimates for the US, the 50 states, and selected urban areas for children ages 19-35 months. The NIS includes a random-digit-dialed telephone survey and a provider record check study. Data are weighted to account for the sample design and to reduce nonresponse and non-coverage biases in order to improve vaccination coverage estimates. Adjustments are made for biases resulting from nonresponse and nontelephone households, and estimation procedures are used to reduce measurement bias. The NIS coverage estimates represent all US children, not just children living in households with telephones. NIS estimates are highly comparable to vaccination estimates derived from the National Health Interview Survey. The NIS allows comparisons between states and urban areas over time and is used to evaluate current and new vaccination strategies.

Objectives: This study was done to assess progress in hepatitis B vaccination of children from 1994 through 1997., Methods: We used data from the National Immunization Survey (NIS), a random-digit-dialed telephone survey that includes a mail survey to verify vaccination providers' records. The NIS is conducted in 78 geographic areas (50 states and 28 selected urban areas) in the United States., Results: A total of 32,433 household interviews were completed in the 1997 NIS. An estimated 83.7% of children aged 19 to 35 months received 3 or more doses of hepatitis B vaccine. Coverage with 3 doses was greater (86.7%) among children in states that had day care entry requirements for hepatitis B vaccination than among children in states without such requirements (83.0%) and was greater among children from families with incomes at or above the poverty level (85.0%) than among children below the poverty level (80.6%). Hepatitis B vaccination of children increased from 1994 through 1996, from 41% to 84%, but coverage reached a constant level of 84% to 85% in 1996/97., Conclusion: Although substantial progress has been made in fully vaccinating children against hepatitis B, greater efforts are needed to ensure that all infants receive 3 doses of hepatitis B vaccine.

Objectives: 1) To determine the proportion of preschool children receiving immunizations from providers enrolled in the Vaccines for Children (VFC) program; 2) to assess whether their immunization providers serve as their medical home for primary care; and 3) to examine the relationship between various provider characteristics and immunization status., Design: Two-phase national survey consisting of parent interviews verified by provider record check., Setting: A total of 78 survey areas (50 states, the District of Columbia, and 27 urban areas)., Patients or Other Participants: Noninstitutionalized children from 19 to 35 months of age in 1997., Interventions: None., Outcome Measures: VFC penetration rate (the percentage of children who received all or some vaccines from a VFC-enrolled provider); the frequency with which children received all or some vaccines within a medical home; the number of parent-reported immunization providers; and 4:3:1:3 up-to-date status at 19 to 35 months of age., Results: OFF 28 298 children interviewed for whom consent to contact providers was obtained, complete provider data were available for 21 522 (76%). Of these children, approximately 75% received all or some immunizations from a VFC-enrolled provider, 73% received all or some immunizations within a medical home, and 75% had one immunization provider. Children received all or some immunizations from a VFC-enrolled provider more frequently when vaccinated by pediatricians versus family physicians or in public facilities versus private practice. After controlling for poverty, immunization coverage varied only slightly with receipt of vaccines from a VFC-enrolled provider, receipt of vaccines within a medical home, and the number of parent-reported providers. Among children vaccinated within a medical home, those vaccinated solely by pediatricians were 1.63 times as likely to be 4:3:1:3 up-to-date than were those vaccinated solely by family physicians after removing the effects of poverty., Recommendations: Greater numbers of children are likely to benefit from an even higher participation rate among immunization providers in the VFC program, particularly among family physicians and private physicians. The public-private collaboration developed by the VFC program should be capitalized on so that public sector resources can help pediatricians and family physicians practice according to the Standards for Pediatric Immunization Practices.