Are there factors other than noncoverage and nonresponse that contribute to the differences in the BRFSS and NHIS direct estimates?
Differences in data collection time, proxy responses, question wording, response modes (telephone vs. in-person), sample design and weighting methodology could cause differences between the BRFSS and NHIS prevalence estimates. For small areas there is also larger sampling error and hence, estimates could differ by chance. Both BRFSS and NHIS are designed to represent the adult population (18 years old or over) living in households. However, the NHIS is a complex, multistage area probability sample that incorporates stratification, clustering, and oversampling of some subpopulations (e.g., Black, Hispanic, and Asian in later years); while the BRFSS is a state-based random-digit-dial (RDD) probability sample that incorporates disproportionate stratified sampling in which listed residential telephone numbers are sampled at a higher rate than unlisted residential telephone numbers. Weighting adjustments are implemented in both surveys to compensate for design-imposed differential selection
