N C H S - N H I S - About This Release (Released 7/2002)

National Health Interview
Survey (NHIS)
Celebrating the First 50 years:
1957 - 2007

Early Release of selected estimates based on data from the 2001 National Health Interview Survey
(Released 7/15/02)

The National Center for Health Statistics (NCHS), Centers for Disease Control and Prevention (CDC) is pleased to present the 4th Early Release of timely data from the National Health Interview Survey (NHIS). In this release, NCHS provides estimates for 12 selected health measures based on new data from the full year 2001 NHIS, with comparisons to estimates from the NHIS back to 1997. For this release, a new measure, personal care needs or activities of daily living (ADL) has been added. The 12 Early Release measures are being published prior to final data editing and weighting to provide improved access to the most recent information from the NHIS.

Objectives: This 4th Early Release provides updates on previously released estimates with data through December 2001. The 12 measures included are: health insurance coverage (including type of coverage), usual place to go for medical care, obtaining needed medical care, influenza vaccination, pneumococcal vaccination, obesity, leisure-time physical activity, current smoking, alcohol consumption, HIV testing, general health status, and personal care needs.

For each selected health measure, a graph is presented showing the trend over time from 1997 through 2001 for the total population, followed by graphs and tables showing estimates by sex, age group, and race/ethnicity based on 12 months of data from the 2001 NHIS. Key findings are highlighted with bulleted text. Data tables providing values displayed in the figures are included at the end of each section. This release also provides updates for age-adjusted estimates for those Early Release measures that are also Healthy People 2010 Leading Health Indicators (lack of health insurance coverage, usual place to go for medical care, influenza vaccination, pneumococcal vaccination, obesity, leisure-time physical activity, and current smoking). Most of these measures are presented in the data table for the first figure of each indicator.

Data source: Data from the full year 2001 NHIS are used to update the Early Release measures in this release. The data are derived from three components of the NHIS: the Family Core questionnaire, which collects information on all family members (data from 100,761 persons); the Sample Adult Core questionnaire, which collects information from one randomly selected adult aged 18 years or over in each family in the NHIS (data from 33,326 adults); and the Sample Child Core questionnaire, which collects information about one randomly selected child in each family with a child in the NHIS (data from 13,579 children). Please visit the NHIS Web site for more detailed information on the structure and content of the NHIS.

Estimation procedures: Using population totals provided by the U.S. Bureau of the Census, sample weights were calculated to provide national estimates for the civilian noninstitutionalized population and to adjust for nonresponse. NCHS creates weights for each calendar quarter of the NHIS sample. The NHIS data weighting procedure has been described in more detail elsewhere (view/download PDF). Because the estimates for the year 2001 are being released prior to final data editing and weighting, they should be considered preliminary and may differ from estimates that will be made later using the final data file. This report presents estimates from the 1997-2000 NHIS that were derived from the final data files for those years (except for Health insurance coverage). A public use file for the 2001 NHIS will be released in December 2002. Please check the NHIS Web site for announcements and more detailed information.

Point and variance estimates were calculated using the SUDAAN software package to account for the complex sample design of the NHIS. The Taylor series linearization method was chosen for variance estimation. All estimates shown meet the NCHS standard of less than 30% relative standard error. Point estimates in some figures are shown with 95% confidence intervals. Differences between percents or rates were evaluated using two-sided significance tests at the .05 level. Terms such as "greater than" and "less than" indicate a statistically significant difference. Terms such as "similar" or "no difference" indicate that the statistics being compared were not significantly different. Lack of comments regarding the difference between any two statistics does not necessarily mean that the difference was tested and found to be not significant. When necessary for comparison purposes, direct standardization was used to estimate age-sex-adjusted or age-adjusted percents using the year 2000 projected U.S. population as the standard population. The age groups used varied depending upon the impact of age on specific measures.

Future plans for Early Release of NHIS estimates: Early Releases of NHIS will update the estimates on a quarterly basis using new data from the NHIS. New measures may be added as work continues and in response to changing data needs. Feedback on the Early Release mechanism and on the estimates is welcome (e-mail). Announcements about Early Releases, new data releases, publications, or corrections related to the National Health Interview Survey (NHIS) will be sent to members of the HISUSERS Listserv. To join, visit the CDC Web site.