Estimates from the 1988 NHIS standard survey and 1988 CHS were compared. The difference was used to calculate an inflation factor to modify the 1997-2000 asthma attack prevalence estimates to make them more comparable with previous asthma period prevalence estimates. We used two different subgroups (referred to as study groups 1 and 2) of 1988 NHIS respondents. As described above, for the 1988 NHIS sample of children aged 0-17 years, one sixth received the standard NHIS asthma question (shown in yellow). One half received the asthma questions from the CHS (shown in orange). Study group 1 contained these two overlapping subsamples of children. Prevalence estimates for the 5,509 children responding to the asthma question on the standard survey (one sixth of the 1988 sample) were compared with prevalence estimates for the 16,624 children responding to the CHS asthma questions (one half of the 1988 sample). Study group 2 contained approximately one twelfth of the NHIS sample (2,805 children) that received both the standard and CHS asthma questions (shown as the hatched area of overlap in the diagram).