Analysis of environmental data with censored observations

Environmental Science & Technology
By: , and 



The potential threats to humans and to terrestrial and aquatic ecosystems from environmental contamination could depend on the sum of the concentrations of different chemicals. However, direct summation of environmental data is not generally feasible because it is common for some chemical concentrations to be recorded as being below the analytical reporting limit. This creates special problems in the analysis of the data. A new model selection procedure, named forward censored regression, is introduced for selecting an appropriate model for environmental data with censored observations. The procedure is demonstrated using concentrations of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine), deethylatrazine (DEA, 2-amino-4-chloro-6-isopropylamino-s-triazine), and deisopropylatrazine (DIA, 2-amino-4-chloro-6-ethylamino-s-triazine) in groundwater in the midwestern United States by using the data derived from a previous study conducted by the U.S. Geological Survey. More than 80% of the observations for each compound for this study were left censored at 0.05 μg/L. The values for censored observations of atrazine, DEA, and DIA are imputed with the selected models. The summation of atrazine residue (atrazine + DEA + DIA) can then be calculated using the combination of observed and imputed values to generate a pseudo-complete data set. The all-subsets regression procedure is applied to the pseudo-complete data to select the final model for atrazine residue. The methodology presented can be used to analyze similar cases of environmental contamination involving censored data.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Analysis of environmental data with censored observations
Series title Environmental Science & Technology
DOI 10.1021/es960695x
Volume 31
Issue 12
Year Published 1997
Language English
Publisher ACS
Contributing office(s) Iowa Water Science Center, Toxic Substances Hydrology Program
Description 5 p.
First page 3358
Last page 3362
Country United States
Online Only (Y/N) N
Additional Online Files (Y/N) N