| Abstract: | 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 ??l/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.A new forward censored regression analysis is introduced for selecting an appropriate model for environmental data with censored observations. The procedure is demonstrated using concentrations of atrazine, deethylatrazine and deisopropylatrazine in groundwater in the midwestern U.S. The summation of atrazine residue can then be calculated using 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. |
| Genre: | Article |
| ProdID: | 70019139 |
| Citation Author: | Liu, S.; Lu, J. -C.; Kolpin, D. W.; Meeker, W. Q. |
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| Citation End Page: | 3362 |
| Citation Issue: | 12 |
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| Citation Language: | English |
| Citation Larger Work Title: | Environmental Science and Technology |
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| Citation Number Of Pages: | 5 |
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| Citation Publisher: | ACS |
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| Citation Search Results Text: | Analysis of environmental data with censored observations; 1997; Article; Journal; Environmental Science and Technology; Liu, S.; Lu, J. -C.; Kolpin, D. W.; Meeker, W. Q. |
| Citation Start Page: | 3358 |
| Citation Volume: | 31 |
| Citation Year: | 1997 |
| Type: | citation/reference |
| Text: | Analysis of environmental data with censored observations; 1997; Article; Journal; Environmental Science and Technology; Liu, S.; Lu, J. -C.; Kolpin, D. W.; Meeker, W. Q. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1021/es960695x |
| Date Other: | Wed, 1 Jan 1997 00:00 -0600 |
| Publisher: | ACS |
