Estimating contaminant loads in rivers: An application of adjusted maximum likelihood to type 1 censored data

This paper presents an adjusted maximum likelihood estimator (AMLE) that can be used to estimate fluvial transport of contaminants, like phosphorus, that are subject to censoring because of analytical detection limits. The AMLE is a generalization of the widely accepted minimum variance unbiased est...

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Bibliographic Details
Published inWater resources research Vol. 41; no. 7
Main Author Cohn, T.A
Format Journal Article
LanguageEnglish
Published 01.07.2005
Subjects
accuracy
adjusted maximum likelihood
data analysis
data censoring
detection
environmental monitoring
Monte Carlo method
overland flow
phosphorus
pollutants
rivers
statistical analysis
water quality
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Summary:This paper presents an adjusted maximum likelihood estimator (AMLE) that can be used to estimate fluvial transport of contaminants, like phosphorus, that are subject to censoring because of analytical detection limits. The AMLE is a generalization of the widely accepted minimum variance unbiased estimator (MVUE), and Monte Carlo experiments confirm that it shares essentially all of the MVUE's desirable properties, including high efficiency and negligible bias. In particular, the AMLE exhibits substantially less bias than alternative censored-data estimators such as the MLE (Tobit) or the MLE followed by a jackknife. As with the MLE and the MVUE the AMLE comes close to achieving the theoretical Frechet-Cramer-Rao bounds on its variance. This paper also presents a statistical framework, applicable to both censored and complete data, for understanding and estimating the components of uncertainty associated with load estimates. This can serve to lower the cost and improve the efficiency of both traditional and real-time water quality monitoring.
ISSN:0043-1397
1944-7973
DOI:10.1029/2004WR003833