Overview of important design issues for a National Human Exposure Assessment Survey

Area of Science:

• Environmental Health Sciences
• Exposure Science
• Risk Assessment

Background:

• Exposure assessment is vital for regulatory decisions, site cleanup, model validation, and cumulative risk evaluation.
• Accurate exposure data provides essential perspective for refining risk estimates.
• The National Human Exposure Assessment Survey (NHEXAS) serves as a case study for exposure monitoring.

Purpose of the Study:

• To discuss critical issues in designing exposure monitoring studies, exemplified by NHEXAS.
• To provide guidance on sampling design strategies for exposure assessors.
• To highlight important nonsampling considerations for reliable exposure assessment.

Main Methods:

• Discussion of sampling design alternatives, including simple random versus multistage designs.
• Analysis of design efficiency, sample size determination for desired precision, and the impact of stratification and oversampling.
• Examination of nonsampling issues: population definition, response rates, and potential interpretation errors.

Main Results:

• Complex sampling designs may offer efficiency gains but require careful planning.
• Stratification and oversampling can reduce sample size needs for specific subpopulations.
• Nonsampling factors like response rates significantly influence the validity and interpretation of monitoring results.

Conclusions:

• Thoughtful consideration of both sampling and nonsampling issues is essential for robust exposure assessment studies.
• Effective survey design, including appropriate sampling strategies and management of nonsampling errors, is key to generating reliable exposure data for regulatory and risk assessment purposes.
• The principles discussed are applicable to NHEXAS and other exposure-monitoring initiatives.