Comment submitted by L. A. Shadoff

Section 6. Feasibility of Quantitative Uncertainty Analysis from NAS Evaluation of the 2003 Reassessment In evaluating uncertainty in a complex process such as undertaken in this study, it would be fruitful to estimate the uncertainty in the many steps required to obtain an estimate. This way, improvement in the process can be simplified by identifying those steps with the greatest variation. For example, in the measurement of the concentration of dioxins in biological samples, there are several sources of error. 1 - In the calibration of the instrumentation used to measure dioxin. 2 - In the multiple steps used to prepare the sample for analysis. 3 - In identifying potential sources of contamination or interference caused by different sample types. I believe it would be fruitful for the agency to require uncertainty analysis for each step in the determination of Toxicity Response. Steps should include, in addition to the overall results: Experimental Design Uncertainty Analysis Uncertainty Sampling Uncertainty Sample Storage Uncertainty Reference Standards Uncertainty Others I am not wise enough to identify. Lewis A. Shadoff, Ph.D. I am a pioneer in the determination of ultra-trace quantities of dioxins in a wide variety of environmental and industrial samples (search the chemical/environmental literature for my name).