1995 National Immunization Survey (NIS) Public-Use Data Release WARNING - DATA USE RESTRICTIONS! Read Carefully Before Use The Public Health Service Act (Section 308(d)) provides that the data collected by the National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention (CDC), may be used only for the purpose of health statistical reporting and analysis. Any effort to determine the identity of any reported case is prohibited by this law. NCHS does all it can to ensure that the identity of data subjects cannot be disclosed. All direct identifiers, as well as any characteristics that might lead to identification, are omitted from the data files. Any intentional identification or disclosure of a person or establishment violates the assurances of confidentiality given to the providers of the information. Therefore, users will: 1. Use the data in these data files for statistical reporting and analysis only. 2. Make no use of the identity of any person or establishment discovered inadvertently and advise the Director, NCHS, of any such discovery (301-458-4500). 3. Not link these data files with individually identifiable data from other NCHS or non-NCHS data files. By using these data, you signify your agreement to comply with the above requirements. Introduction In 1992 the Childhood Immunization Initiative (CII) was established to 1) improve the delivery of vaccines to children; 2) reduce the cost of vaccines for parents; 3) enhance awareness, partnerships, and community participation; 4) improve vaccinations and their use; and 5) monitor vaccination coverage and occurrences of disease. Subsequently the Healthy People 2000 and 2010 objectives established the goal of having at least 90% of 2-year-old children fully vaccinated with the recommended schedule of vaccines. To fulfill the CII mandate of monitoring vaccination coverage and marking progress toward achieving those goals, the National Immunization Survey (NIS) has been implemented by the National Immunization Program and the National Center for Health Statistics, Centers for Disease Control and Prevention (CDC), and its contractor, Abt Associates Inc. The target population for the NIS is children aged 19 to 35 months living in the United States at the time of the interview. The official coverage estimates reported from the NIS are rates of being up-to-date with respect to the recommended numbers of doses of all recommended vaccines. These vaccines and their recommended numbers of doses are: diphtheria and tetanus toxoids and pertussis vaccine (DTP), 4 doses; poliovirus vaccine (polio), 3 doses; measles-containing vaccine (MCV), 1 dose; Haemophilus influenzae type b vaccine (Hib), 3 doses; and hepatitis B vaccine (Hep B), 3 doses. In addition to these vaccines, interest focuses on coverage rates for vaccine series, including the 4:3:1:3 series(4 DTP, 3 polio,1 MCV, and 3 Hib). The NIS has collected data on each of these vaccines from its start in 1994. Sample Design The NIS uses a random-digit-dialing (RDD) telephone survey to identify households containing children in the target age range and interview an adult who is knowledgeable about the child's vaccinations. With the consent of the child's parent or guardian, the NIS also contacts (by mail) the child's health care providers to request information on vaccinations from the child's medical records. Samples of telephone numbers are drawn independently, for each calendar quarter, within 78 Immunization Action Plan (IAP) areas. Of the 78 IAP areas, 28 (including the District of Columbia) are urban areas. The remaining 50 are either an entire state or a "rest of state" IAP area (where the state contains one or more urban IAP areas). This design makes it possible to produce annualized estimates of vaccination coverage levels within each of the 78 IAP areas. Further, by using the same data collection methodology and survey instruments in all IAP areas, the NIS produces vaccination coverage levels that are comparable among IAP areas and over time. The target sample size in each IAP area is designed to achieve an approximately equal number of children with completed telephone interviews in all 78 IAP areas. Content of the NIS Household Questionnaire Screening questions aim to identify households that contain at least one child 19 to 35 months of age. For each such child the following information is collected: date of birth, sex, name, and availability of written shot records. The interview then continues with the person who is the most knowledgeable about the child's immunization history. When a shot card is available during the interview, Section A asks the respondent to refer to it and to report, for each vaccine, the number of shots received and the date on which each shot was administered. If a shot record is not available, Section B asks the respondent to recall, for each of the recommended vaccines, whether the child has ever had a shot for that vaccine and, if so, how many shots the child has received. Section C obtains information about the household (number of adult and child residents, place of residence at child's birth, income), the child (Hispanic origin, race), and the respondent and/or mother (respondent's relationship to the child; mother's marital status, Hispanic origin, race, and education). Section D concludes the interview by requesting consent to contact the child's vaccination providers. If consent is obtained, identifying information (name, address, and telephone number) for the vaccination provider(s) is recorded. Content of the NIS Provider Questionnaire The provider survey mails an Immunization History Questionnaire (IHQ) to each provider for whom the address is adequate. The IHQ is designed to be simple and brief, to minimize burden on providers and to encourage participation in the survey. It consists of two pages. A label with identifying information about the child (name and date of birth, and the full name of the parent) is affixed to Page 1, which consists of a grid for recording dates of vaccinations. Page 2, on the back of Page 1, contains questions about the facility and vaccination provider. Guidelines for Data Users The NIS Public-Use File (PUF) can be used to form national, state and IAP-area estimates of vaccination coverage rates. As the 1995 NIS PUF Data User's Guide explains, information in the data file can be used to calculate standard errors of the vaccination coverage rates that reflect the complex sample design of the NIS. The file includes IAP area and state identifiers. The sample is stratified by the 78 IAP areas, and the IAP area identifier is a key variable for obtaining standard errors. Demographic and socioeconomic variables in the file can be used to obtain national vaccination coverage rates for subgroups of the population. Data users should, however, be aware that estimates for such subgroups at the state or IAP-area level will generally have large standard errors because of the small sample sizes. General Variable Information The variables in the NIS PUF fall into two major groupings: 1) variables that apply to all children with completed household interviews (n=31,997 in 1995) and 2) variables that apply only to children with adequate provider data (n=16,183 in 1995). The phrase "children with adequate provider data" refers to children for whom sufficient vaccination history information is obtained from their providers to determine whether they are up-to-date with respect to the recommended vaccination schedule. Data users are advised of the following: the variables form 9 categories (weights, household report of vaccinations, demographic and socioeconomic characteristics, geographic identifiers, number of providers identified, number of providers responding, provider characteristics, provider up-to-date vaccination indicators, and age at vaccination), some variables have been top- or bottom-coded to reduce risk of disclosure, and values were imputed for selected variables using a hot-deck procedure. Composite Variables A number of composite variables are constructed and included in the NIS PUF. Household composite variables include up-to-date status on individual vaccinations, race of child and mother, household income, and up-to-date status on several vaccination series. At the child level, the provider data are used to create the number of doses received for each type of vaccine, up-to-date indicator variables for each individual vaccine and for series of vaccines, and age in days and age in months of the child when each vaccination was administered. Composite variables for provider characteristics include facility type, types of care offered, participation in the Vaccines for Children program, and medical home. Missing-Value Codes In general, missing values for household variables are: 6, 96 DON'T KNOW 7, 97 REFUSED Some household variables contain blanks if the question was not asked. IHQ variables generally do not have specific missing-value codes. For example, if a provider failed to answer the question on types of care provided, the response category variables for that question would be blank. For provider-reported vaccination dates before the date of birth of the child, the age in months and age in days variables are recoded to -1. For provider-reported vaccination dates after 36 months of age, the age in months variables are recoded to 40. For the corresponding provider-reported vaccination dates after 1125 days of age, the age in days variables are recoded to 1210. Use of the NIS Sampling Weights The NIS PUF contains two child-level weights. HY_WGT is the household weight variable for each child. It should be used to form estimates from the children with completed household interviews. This weight reflects the stratified sample design and also adjusts for unit nonresponse, for poststratification to population control totals, and for the exclusion of nontelephone children from the NIS. Children with adequate provider data (PDAT = 1) also have a second weight, variable W0. This weight should be used to form estimates of vaccination coverage rates. Order of Records in the Data File All records in the 1995 NIS public-use data file have been sorted, first by the unique household identification number (SEQNUMHH). Within the household identification number, the data file is further sorted by the unique child identification number (SEQNUMC). SEQNUMC consists of 6 digits: the first five digits are SEQNUMHH, and the sixth digit uniquely identifies the child within the household. Documentation For more information about the 1995 NIS PUF, data users should consult the 1995 NIS PUF Data User's Guide. Users of these data must review that descriptive and explanatory documentation to analyze the data correctly. File documentation describing each data variable, its associated response values, and explanatory notes is included in the 1995 NIS PUF Code Book. These documents are available in PDF. Documents in PDF can be viewed with Adobe Acrobat software. The Adobe Acrobat Reader can be downloaded from the Adobe Acrobat Web site at: http://www.adobe.com/prodindex/acrobat/readstep.html. The 1995 NIS PUF Data User's Guide provides more-specific detail about the design of the 1995 NIS, the weighting and estimation procedures, and other important information needed for analyzing these data. The 1995 NIS PUF Code Book contains a listing of variables (in data-file-position order), the variable responses, and either unweighted frequencies of categorical variables or unweighted summary statistics for continuous variables. Estimates of vaccination coverage rates from the 1995 NIS are available at: http://www.cdc.gov/nip/coverage/ Content of the 1995 NIS PUF The 1995 NIS public-use data file is available in ASCII format. The actual file is in a compressed format and can be expanded using WinZip or other software. A SAS program (in ASCII format) is provided to facilitate reading the ASCII data file and creating a SAS dataset. The SAS program contains, for each variable in the ASCII file, the variable name, its starting and ending positions, labels, and formats. Available files are: NAME.TYPE File Description --------------------------------------------------------------------- 95README.TXT 1995 ReadMe File (this text) NISPUF95.DAT 1995 NIS PUF data (ASCII format) NISCBK95.PDF 1995 NIS PUF Code Book (Adobe Acrobat format) NISDUG95.PDF 1995 NIS PUF Data User's Guide (Adobe Acrobat format) NISPUF95.SAS SAS program to read data, create format library, and attach formats to variables The ASCII file NISPUF95.DAT can be used for processing by statistical software packages that accept ASCII-formatted input, or it can be transferred to another computer for processing. NOTE: The 1995 NIS files are large. Please use caution and check the capacity of your disk drive before downloading them. File File Name Description Format File Size (KB) NISPUF95.DAT Data File ASCII 31,685 NISCBK95.PDF Code Book PDF 221 NISDUG95.PDF User's Guide PDF 325 NISPUF95.SAS SAS Program ASCII 35 The 1995 NIS data files are also located at: ftp://ftp.cdc.gov/pub/Health_Statistics/NCHS/Datasets/NIS/ Guidelines for Citation of Data With the goal of mutual benefit, the National Center for Health Statistics (NCHS) and the National Immunization Program (NIP) request that recipients of data files cooperate in certain actions related to their use. Any published material derived from these data should acknowledge CDC (NCHS and NIP) as the original data source and use "NIS" in the title or as a keyword in the abstract. The suggested citation to appear at the bottom of all tables is as follows: Source: CDC, NIP and NCHS (2002), 1995 National Immunization Survey. The reference for the 1995 NIS data file is: U.S. Department of Health and Human Services (DHHS). National Center for Health Statistics. The 1995 National Immunization Survey, CD-ROM No. 5. Hyattsville, MD: Centers for Disease Control and Prevention, 2002. Published material should also include a disclaimer that attributes any analyses, interpretations, or conclusions reached to the author (recipient of the data file) and not to NCHS, which is responsible only for the initial data. Consumers who wish to publish a technical description of the data should ensure that the description is consistent with that published by NCHS. Although the data files have been edited carefully, errors may be detected. Please notify NCHS staff (301-458-4636) of any errors in the 1995 NIS data or documentation and refer to the NCHS website at www.cdc.gov/nis for updates to the NIS data files.