JSM 2004 - Toronto

Abstract #300908

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Activity Number: 20
Type: Contributed
Date/Time: Sunday, August 8, 2004 : 2:00 PM to 3:50 PM
Sponsor: Section on Statistics and the Environment
Abstract - #300908
Title: Estimation of Limits of Detection in the Analysis of Environmental Data
Author(s): Changjian Jiang*+
Companies: Monsanto
Address: 700 Chesterfield Pkwy. W, Chesterfield, MO, 63017,
Keywords: Box-Cox transformation ; censored data ; maximum likelihood ; limit of detection ; confidence limits
Abstract:

We present a statistical model for the estimation of the limit of detection in environmental studies, where the mean and standard deviation of the responses for an analyte almost always depend on the actual concentration and normality of the distribution is questionable. The proposed method applies to a set of fortified samples. It assumes the dependence of the means and standard deviations of the responses on the concentration being linear after the Box-Cox transformation on both the responses and the fortification levels with power selections based on the data. Limit of detection and other environmental study measures, expressed as functions of the model parameters, can be estimated by maximizing the likelihood function using the SAS procedure NLMIXED.

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