About This Early Release

Early Release of Selected Estimates Based on Data From the January-March 2005 National Health Interview Survey

In this release, the National Center for Health Statistics (NCHS) updates estimates for 15 selected health measures based on data from the January-March 2005 National Health Interview Survey (NHIS) and presents estimates from 1997 through 2004 for comparison. New for this release, the indicator that previously presented estimates for receipt of influenza shots by adults has been expanded to include influenza vaccinations administered by nasal spray. In addition, estimates of both types of influenza vaccinations for children are provided for the first time in the Early Release. The 15 Early Release measures are being published prior to final data editing and final weighting to provide access to the most recent information from the NHIS. The estimates will be updated on a quarterly basis as each new quarter of the NHIS data becomes available.

The 15 measures included are lack of health insurance coverage and type of coverage, usual place to go for medical care, obtaining needed medical care, receipt of an influenza vaccination, pneumococcal vaccination, obesity, leisure-time physical activity, current smoking, alcohol consumption, human immunodeficiency virus testing, general health status, personal care needs, serious psychological distress, diagnosed diabetes, and asthma episodes and current asthma.

For each selected health measure, a figure is presented showing the trend over time from 1997 through January-March 2005 for the total population, followed by figures and tables showing estimates by age group and sex based on data from the January-March 2005 NHIS. Also, estimates (often adjusted by age or sex or both) are provided for three race/ethnicity groups (Hispanic; non-Hispanic white, single race; and non-Hispanic black, single race) using data from the January-March 2005 NHIS. Key findings are highlighted with bulleted text. Data tables providing values displayed in the figures are included at the end of each section. In addition to providing age-adjusted estimates for Early Release measures that are also Healthy People 2010 Leading Health Indicators (lack of health insurance coverage, usual place to go for medical care, receipt of an influenza vaccination, pneumococcal vaccination, obesity, leisure-time physical activity, and current smoking), this release provides overall age-adjusted and crude estimates by sex for all indicators (1). The NHIS questions used to define the selected health measures are included in table I in the Appendix.

Race/ethnicity category

The race/ethnicity categories for data years beginning in 2003 are defined using the new (1997) standards for the classification of Federal data on race/ethnicity promulgated by the Office of Management and Budget (OMB) (2). Subsequent to the Early Releases based on data through 2002, the categories "non-Hispanic white" and "non-Hispanic black" have been changed to "not Hispanic white, single race" and "not Hispanic black, single race." The terms "Hispanic" and "Black" have been changed to "Hispanic or Latino'' and "black or African American,'' respectively. However, the text and figures use shorter terms for conciseness. For example, the category "not Hispanic or Latino, white, single race" in the tables is referred to as "non-Hispanic white" in the text. Race/ethnicity-specific estimates for years prior to 2003 released previously were based on the 1977 OMB standards and, therefore, are not strictly comparable with estimates for 2003. However, the changes in the OMB standards have little effect on the health estimates reported here. See tables XI and XII in Health, United States, 2003 (3) for a comparison of estimates for cigarette smoking and private health insurance coverage using both the 1977 and 1997 OMB standards. In addition, beginning with the 2003 NHIS (and first implemented in the September 2004 Early Release), NHIS editing procedures were changed to maintain consistency with the U.S. Census Bureau procedures for collecting and editing data on race/ethnicity. These changes reflect the elimination of "Other race" as a separate race response. This response category is treated as missing, and the race is imputed if this was the only race response. In cases where "Other race" was mentioned along with one or more OMB race groups, the "Other race" response is dropped, and the OMB race group information is retained. This change is not expected to have a substantial effect on the estimates.

Data source

The data are derived from the three components of the 1997-January-March 2005 NHIS: the Family Core (collects information on all family members in each household), the Sample Adult Core (collects information from one randomly selected adult aged 18 years and over in each family), and the Sample Child Core (collects information on one randomly selected child in each family with a child). Data analyses for the January-March 2005 NHIS were based on 21,853 persons in the Family Core, 7,418 adults in the Sample Adult Core, and 2,862 children in the Sample Child Core. Visit the NHIS Web site for more information on the design, content, and use of the NHIS.

Transition to the 2000 census-based weights

Estimates were calculated by using the NHIS sample weights, which were calibrated to 2000 census-based totals for sex, age, and race/ethnicity of the U.S. civilian noninstitutionalized population. In Early Release reports released before September 2003, the weights for the 1997-2002 NHIS data were derived from 1990 census-based postcensal population estimates. Beginning with the 2003 data, the NHIS has transitioned to weights derived from the 2000 census-based population estimates. The impact of this transition was assessed for data from the 2000-02 NHIS by comparing estimates using the 1990 census-based weights with those using the 2000 census-based weights. The results are presented in tables II and III in the Appendix. Although the changes for all selected measures are within 1 percentage point, the 2000-02 estimates for all selected measures have been recalculated in this report using weights derived from the 2000 census. Information needed to revise the 1997-99 estimates based on intercensal estimates is not yet available.

Estimation procedure

NCHS creates weights for each calendar quarter of the NHIS sample. The NHIS data weighting procedure has been described in more detail elsewhere (Design and Estimation for the National Health Interview Survey, 1995–2004 [PDF - 300 KB]). Because the estimates for January-March 2005 are being released prior to final data editing and final weighting, they should be considered preliminary and may differ slightly from estimates made later using the final data files. Except for health insurance coverage, estimates from the 1997-2003 NHIS were derived from the final data files for those years. However, as mentioned previously, estimates for 2000-02 were recalculated in this report using the 2000 census-based weights that were not included in the final files. See "Health Insurance Coverage" (section 1) in this release for details on special data editing for health insurance variables. For NHIS announcements and more detailed information, check the NHIS Web site .

Point estimates and estimates of their variances 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 having less than or equal to 30% relative standard error. Point estimates in some figures and tables are accompanied by 95% confidence intervals. Differences between percentages or rates were evaluated using two-sided significance tests at the 0.05 level. Terms such as "greater than" and "less than" indicate a statistically significant difference. Terms such as "similar" and "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 suggest that the difference was tested and found to be not significant. Direct standardization was used to calculate age-sex-adjusted percentages for three race/ethnicity groups using the 2000 projected U.S. standard population (4). For the prevalence of obesity, only age-adjusted sex-specific percentages are presented because the race/ethnicity pattern in obesity prevalence differs by sex. Similarly, only sex-adjusted age-specific prevalences are presented for the asthma measures because the race/ethnicity patterns in asthma episodes and current asthma differ by age. The age groups used for standardization varied depending upon the impact of age on the specific measure. Rates presented are crude rates unless otherwise stated.

Health insurance

Two additional questions were added to the health insurance section of the NHIS beginning in quarter 3 of 2004 to reduce potential errors in reporting Medicare and Medicaid status. Persons aged 65 years and over not reporting Medicare coverage were asked explicitly about Medicare coverage. Persons under age 65 years with no reported coverage were asked explicitly about Medicaid coverage. For this report, estimates that exclude the two additional questions are labeled "Method 1," and estimates that include the additional questions are labeled "Method 2." Estimates for years 1997-2003 in this report are all generated using Method 1. Estimates for 2004 are presented using Method 2 in figures and both Method 1 and Method 2 in tables. Estimates for January-March 2005 are calculated using Method 2. Statements about trends or comparisons for 1997 through 2003 are based on estimates calculated using Method 1. Comparisons between 2004 and 2005 are calculated using Method 2. Statements assessing trends that encompass years both prior to and after 2004 take both methodologies into account. Conclusions regarding trends are not made in cases where using one method yields a different result than the same trend analysis using the other method. It should be noted that although both methodologies may yield the same conclusion, the extent of the increasing or decreasing trend is larger using one method compared to the other method.

Although the January-March 2005 estimates based on Method 1 methodology are not presented in the tables or figures, these estimates were calculated to assess the effect of adopting Method 2 in the calculations for these estimates. As was the case for comparisons of the estimates for quarters 3 and 4 of 2004, from January through March 2005, the estimates (weighted) for persons without health insurance coverage were lower using Method 2 (9.7% vs. 8.6% for persons under 18 years of age, 19.5% vs. 19.3% for adults 18-64 years of age, and 2.0% vs. 1.0% for persons 65 years of age and over). The estimates for public coverage were higher using Method 2 (29.7% vs. 30.8% for children under 18 years of age, 11.3% vs. 11.5% for adults 18-64 years of age, and 90.7% vs. 96.1% for persons 65 years of age and over). However, these differences between the estimates were only statistically significant for persons aged 65 years and over. There is no impact on the two additional questions on the estimates for private coverage.

Future plans for Early Release of NHIS estimates

The NCHS Early Release Program updates and releases estimates about 6 months after NHIS data collection has been completed for each quarter (5). These releases are tentatively scheduled for March, June, September, and December. 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, other 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 NCHS Listservs page.

Suggested Citation

Schiller JS, Martinez M, Barnes P. Early release of selected estimates based on data from the January-March 2005 National Health Interview Survey. National Center for Health Statistics. /nchs/nhis.htm. September 2005.