Technical Appendix

About the Survey

The National Survey of Children’s Health (NSCH) was fielded using the State and Local Area Integrated Telephone Survey (SLAITS) mechanism. SLAITS is conducted by the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention (CDC). It uses the same large-scale random-digit-dial sampling frame as the CDC’s National Immunization Survey.¹

Approximately 1.9 million telephone numbers were randomly generated for inclusion in the NSCH. After eliminating numbers that were determined to be nonresidential or nonworking, the remaining numbers were called to identify households with children less than 18 years of age. From each household with children, one was randomly selected to be the focus of the interview.

The respondent was the parent or guardian in the household who was most knowledgeable about the health and health care of the children under 18 years of age. For 79 percent of the children, the respondent was the mother. Respondents for the remaining children were fathers (17 percent), grandparents (3 percent), or other relatives or guardians (1 percent). Surveys were conducted in English and Spanish. Overall, 5.9 percent of the interviews were completed in Spanish.

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Data Collection

Data collection began on January 29, 2003 and ended on July 1, 2004, with interviews conducted from telephone centers in Chicago, Illinois; Las Vegas, Nevada; and Amherst, Massachusetts. A computer-assisted telephone interviewing system was used to collect the data. A total of 102,353 interviews were completed for the NSCH, with 87 percent of the interviews completed in 2003. The number of completed interviews varied by state, ranging from 1,848 in New Mexico to 2,241 in Louisiana and Ohio, with one exception: Only 1,483 interviews were completed in Utah.

The cooperation rate, which is the proportion of interviews completed after a household was determined to include a child under age 18, was 68.8 percent. The national weighted response rate, which includes the cooperation rate as well as the resolution rate (the proportion of telephone numbers identified as residential or nonresidential) and the screening completion rate (the proportion of households successfully screened for children), was 55.3 percent.

Several efforts were made to increase response rates, including sending letters to households in advance to introduce the survey, leaving toll-free numbers on potential respondents’ answering machines to allow them to call back, and providing small monetary incentives for those households with children who initially declined to participate.

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Data Analysis

For producing the population-based estimates in this report, the data records for each interview were assigned a sampling weight. These weights are based on the probability of selection of each household telephone number within each State, with adjustments that compensate for households that have multiple telephone numbers, for households without telephones, and for nonresponse.

With data from the U.S. Bureau of the Census, the weights were also adjusted by age, sex, race, ethnicity, household size, and educational attainment of the most educated household member to provide a dataset that was more representative of each State’s population of noninstitutionalized children less than 18 years of age. Analyses were conducted using statistical software that accounts for the weights and the complex survey design. Responses of “don’t know” and “refuse to answer” were counted as missing data.

Children’s areas of residence were classified according to the Rural-Urban Commuting Areas (RUCAs) developed by the Federal Office of Rural Health Policy.² The 10 RUCA codes were grouped into three categories. “Urbanfocused areas” (RUCA codes 1.0, 1.1, 2.0, 2.1, 2.2, 3.0, 4.1, 5.1, 7.1, 8.1, and 10.1) include metropolitan areas and surrounding towns from which commuters flow to an urban area; large rural areas (RUCA codes 4.0, 5.0, and 6.0) include large towns (“micropolitan” areas) with populations of 10,000 to 49,999 and their surrounding areas; and small or isolated rural areas (all remaining codes) include small towns with populations of 2,500 to 9,999 and their surrounding areas.

Children were classified by race and ethnicity in six categories: non-Hispanic White, non-Hispanic Black, Hispanic, non-Hispanic American Indian/Alaska Native (alone or in combination with other races), other single races, and other combined races. Racial and ethnic groups are mutually exclusive; that is, data reported for White, Black, multiracial, and children of other races do not include Hispanics, who may be of any race. These categories differ from the racial aggregation method recommended by the Office of Management and Budget, which keeps intact the five single-race categories and includes the four double-race combinations that are most frequently reported. This analysis did not employ these nine groups because sample sizes did not support it. However, a separate category was included for American Indian/Alaska Natives, as well as those who are of other races, because their well-known health risks may vary by locality.

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Accuracy of the Results

The data from the NSCH are subject to the usual variability associated with sample surveys. Small differences between survey estimates may be due to random survey error and not to true differences among children or across States.

The precision of the survey estimates is based on the sample size and the measure of interest. Estimates at the national level will be more precise than estimates at the urban/rural level, and those for all children will be more precise than estimates for subgroups of children (for example, children 0-5 years of age or children within the same race). For national estimates of the health and health care for all children, the maximum margin of error is 0.6 percent. For estimates reported by area of residence for all children, the maximum margin of error is 1.6 percent.

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Availability of the Data

All data collected in the NSCH are available to the public on the NCHS and MCHB Web site, except for data suppressed to protect the confidentiality of the survey subjects. Data documentation and additional details on the methodology³ are available from the National Center for Health Statistics.

Interactive data queries are possible through the Data Resource Center (DRC) for the NSCH. The DRC provides immediate access to the survey data, as well as resources and assistance for interpreting and reporting findings.

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Data Limitations

The findings presented here are based entirely on parental reports; however, the majority of questions have been tested for validity when reported by parents. In some cases, data are missing for some respondents for some questions. In addition, certain populations of children, such as those with no telephones at home or those living in an institutional setting, are excluded from the survey.

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1 Zell ER, Ezzati-Rice TM, Battaglia MP, Wright RA. National immunization survey: The methodology of a vaccination surveillance system. Public Health Reports 115:65-77. 2000.

2 USDA Economic Research Service and the WWAMI Rural Health Research Center. What are Rural-Urban Commuting Areas? http://fammed.washington.edu/wwamihrc/rucas/rucas.html

3 Blumberg SJ, Olson L, Frankel M, et al. Design and Operation of the National Survey of Children’s Health, 2003. National Center for Health Statistics. Vital Health Stat 1(43). 2005.