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RECORD NUMBER: 9 OF 9

OLS Field Name OLS Field Data
Main Title Testing for Trends When There Are Changes in Methods.
Author Newell, A. D. ; Blick, D. J. ; Hjort, R. C. ;
CORP Author ManTech Environmental Technology, Inc., Corvallis, OR.;Corvallis Environmental Research Lab., OR.
Publisher c1993
Year Published 1993
Report Number EPA/600/J-93/405;
Stock Number PB93-236420
Additional Subjects Water quality data ; Water pollution sampling ; Data collection ; Standards ; Environmental monitoring ; Trends ; Concentration(Composition) ; Calibrating ; Revisions ; Mathematical models ; Surveys ; Graphs(Charts) ; Statistical analysis ; Long term effects ; Reprints ; Kendall tau test
Holdings
Library Call Number Additional Info Location Last
Modified
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Status
NTIS  PB93-236420 Most EPA libraries have a fiche copy filed under the call number shown. Check with individual libraries about paper copy. 11/22/1993
Collation 14p
Abstract
Data from monitoring projects often include sampling or analytical changes that preclude trend analysis on the entire period of record. A modification of the nonparametric Kendall's test for monotonic trends, which accounts for such changes in the period of record, is described here. This approach blocks the data so that only data collected or analyzed under similar circumstances are compared. Alternatively, when appropriate data exist, data collected using the old method may be calibrated to values expected from the new method. Traditional trend tests may then be applied to resulting data sets. Results from simulations assessing both the power of the blocked test and the standard test performed on calibrated data are presented. The power of the blocked test exceeded the power of the calibration approach only when the calibration error was extremely large. Both the blocking and calibration approaches were applied to and compared for chemical data from Vermont lakes. (Copyright (c) 1993 Kluwer Academic Publishers.)