Sampling design, response rates, and analysis weights for the National Human Exposure Assessment Survey (NHEXAS) in EPA Region 5

For the Phase I field test of the National Human Exposure Assessment Survey (NHEXAS) in U.S. Environmental Protection Agency (EPA) Region 5, this pape r presents the survey sampling design, the response rates achieved, and the sample weighting procedure implemented to compensate for unit nonresponse. To enable statistically defensible inferences to the entire region, a samp le of about 250 members of the household population in EPA Region 5 was sel ected using a stratified multistage probability-based survey sampling desig n. Sample selection proceeded in four nested stages: (1) sample counties; ( 2) area segments based on Census blocks within sample counties; (3) housing units (HUs) within sample segments; and (4) individual participants within sample households. Each fourth-stage sample member was asked to participat e in 6 days of exposure monitoring. A subsample of participants was asked t o participate in two rounds of longitudinal follow-up data collection. Appr oximately 70% of all sample households participated in household screening interviews in which rosters of household members were developed. Over 70% o f the sample subjects selected from these households completed the Baseline Questionnaire regarding their demographic characteristics and potential fo r exposures. And, over 75% of these sample members went on to complete at l east the core environmental monitoring, including personal exposures to vol atile organic compounds (VOCs) and tap water concentrations of metals. The sample weighting procedures used the data collected in the screening interv iews for all household members to fit logistic models for nonresponse in th e later phases of the study. Moreover, the statistical analysis weights wer e poststratified to 1994 State population projections obtained from the Bur eau of the Census to ensure consistency with other statistics for the Regio n.