Nonparametric statistical methods for comparing two sites based on data with multiple nondetect limits

Water Resources Research
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Abstract

As concern over the effects of trace amounts of pollutants has increased, so has the need for statistical methods that deal appropriately with data that include values reported as “less than” the detection limit. It has become increasingly common for water quality data to include censored values that reflect more than one detection limit for a single analyte. For such multiply censored data sets, standard statistical methods (for example, to compare analyte concentration in two areas) are not valid. In such cases, methods from the biostatistical field of survival analysis are applicable. Several common two‐sample censored data rank tests are explained, and their behaviors are studied via a Monte Carlo simulation in which sample sizes and censoring mechanisms are varied under an assumed lognormal distribution. These tests are applied to shallow groundwater chemistry data from two sites in the San Joaquin Valley, California. The best overall test, in terms of maintained α level, is the normal scores test based on a permutation variance. In cases where the α level is maintained, however, the Peto‐Prentice statistic based on an asymptotic variance performs as well or better.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Nonparametric statistical methods for comparing two sites based on data with multiple nondetect limits
Series title Water Resources Research
DOI 10.1029/WR024i012p02087
Volume 24
Issue 2
Year Published 1988
Language English
Publisher American Geophysical Union
Contributing office(s) California Water Science Center
Description 12 p.
First page 2087
Last page 2098
Country United States
State California
Other Geospatial San Joaquin Valley