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LIMITATIONS ON THE USES OF MULTIMEDIA EXPOSURE MEASUREMENTS FOR MULTIPATHWAY EXPOSURE ASSESSMENT - PART I: HANDLING OBSERVATIONS BELOW DETECTION LIMITS
Citation:
CLAYTON, C. A., P. L. MOSQUIN, E. D. PELLIZARRI, AND J. J. QUACKENBOSS. LIMITATIONS ON THE USES OF MULTIMEDIA EXPOSURE MEASUREMENTS FOR MULTIPATHWAY EXPOSURE ASSESSMENT - PART I: HANDLING OBSERVATIONS BELOW DETECTION LIMITS. QUALITY ASSURANCE: GOOD PRACTICE, REGULATION, AND LAW. Taylor & Francis, Inc., Philadelphia, PA, 10(3-4):123-159, (2004).
Impact/Purpose:
The NHEXAS analysis projects being conducted by NERL address the following scientific issues/questions:
- Do exposure distributions vary by demographic group?
- What is the impact of censoring (BDL) on multimedia distributions and associations?
- Which questionnaire/diary items are most useful in explaining variability or identifying "high exposure" groups?
- How do exposure classifications and measurements compare in their ability to explain variability in exposures and biomarkers?
- Can changes in exposures over time be explained by dietary and questionnaire/activity information?
- How well do NHEXAS findings compare with existing models/assessments (e.g., NATA)?
Description:
Multimedia data from two probability-based exposure studies were investigated in terms of how censoring of non-detects affected estimation of population parameters and associations. Appropriate methods for handling censored below-detection-limit (BDL) values in this context were unclear since sampling weights were involved and since bivariate associations/measures were of interest. Both simple substitution (e.g., using to = or 2/3 of the detection limit (DL) for BDL values) and truncation-based strategies were investigated by creating some artificial DLs and comparing resultant estimates with the original studies' uncensored results. The substitution methods generally outperformed the truncation methods, with the (2/3)DL substitution generally performing best.
The United States Environmental Protection Agency through its Office of Research and Development funded and collaborated in the research described here under contract number 68-D-99-008 and assistance agreement number CR821902 to Research Triangle Institute. It has been subjected to Agency review and approved for publication.