Some of the detailed subgroups are not identified on all of the data tapes. Section 1.3 identifies those subgroups that are not fully described on the data records, and indicates whether the omitted subpopulations were not identified in the interview or, if obtained, were not entered into the data tape. In addition, there currently are slight variations among surveys in the way the race/ethnicity questions are worded but, except for the birth registration system, the surveys appear to be reasonably consistent in their classifications. NHANES III probed more intensively than most other surveys to identify persons whose ancestors migrated from Mexico, even though, at this time, they do not consider themselves Mexican-Americans. However, the intensive probing was dropped for current NHANES. It also is important to note that birth certificates ask for race/ethnicity of mother and father, but not of child. Since information for the father is less likely to be available, published data on births are tabulated by the race/ethnicity of the mother, which can introduce some error into the calculation of rates where the numerators are from the NVS-Natality files, but denominators are drawn from other data systems. This inconsistency, however, is not present for infant mortality rates where the linked birth/infant death data set is used and data are tabulated by the mothers race.
The differences among surveys are expected to largely disappear when the revised OMB standards for collecting race/ethnic data, which permit respondents with mixed ancestry to choose more than one race, are implemented. Most surveys will be converting to the new standards over the course of the next 4 or 5 years. The new classifications will bring greater consistency among surveys. NHIS has been collecting data on multiple race identification since 1982, and NHANES currently follows the NHIS approach. To reduce possible problems of historical comparability, NCHS, BLS, and the U.S. Census Bureau have carried out research on strategies to bridge the changes created by the shift to the new classification of race/ethnicity. The proposed OMB revisions in the standards for the federal collection of race/ethnicity are shown in Appendix C, Task 2 Report.