Use of observations below detection limit for model calibration
Censored (nondetect) values occur when chemical concentrations in water samples are near or below the level that can be measured by an analysis method. It is common to either delete or substitute values for nondetect observations for use in model calibration, but this practice can bias the estimated...
| Veröffentlicht in: | Ground water. - 1979. - 47(2009), 2 vom: 01. März, Seite 228-36 |
|---|---|
| 1. Verfasser: | |
| Weitere Verfasser: | |
| Format: | Online-Aufsatz |
| Sprache: | English |
| Veröffentlicht: |
2009
|
| Zugriff auf das übergeordnete Werk: | Ground water |
| Schlagworte: | Journal Article Research Support, Non-U.S. Gov't Water 059QF0KO0R |
| Zusammenfassung: | Censored (nondetect) values occur when chemical concentrations in water samples are near or below the level that can be measured by an analysis method. It is common to either delete or substitute values for nondetect observations for use in model calibration, but this practice can bias the estimated parameter values and the model predictions. A more realistic representation of the system is obtained from the calibration if we include such observations in a manner reflecting that we know only the value is below the detection limit. Consequently, we propose use of the censored-residual approach to including nondetect values as observations for calibration. In this approach, residuals are calculated as the detection limit minus the simulated value when the simulated value exceeds the detection limit, and the residual is assigned a value of zero when the simulated value is below the detection limit. The new censored-residual approach is particularly advantageous when calibrating transport models to low concentration data |
|---|---|
| Beschreibung: | Date Completed 16.06.2009 Date Revised 21.11.2013 published: Print-Electronic Citation Status MEDLINE |
| ISSN: | 1745-6584 |
| DOI: | 10.1111/j.1745-6584.2008.00515.x |