Statistics for Censored Environmental Data

**NADA Course Outline**

Day 1

Types of Reporting Limits

detection and quantitation limits

implications for data analysis

Storing Nondetects in a Database

three standard formats

Plotting Data with Nondetects

censored boxplots

censored probability plots

scatterplots with nondetects

survival curves

Overview: The Three Approaches

ROS (probability plotting)

maximum likelihood

nonparametric methods

why not to substitute (fabricate) data

Estimating Descriptive Statistics

what's the mean of <1, 5 <10 and 17?

parametric methods

Kaplan-Meier and other nonparametric methods

why Cohen and Delta-lognormal are “old technology”

Computing Interval Estimates

how to compute confidence intervals with nondetects

UCLs for censored data

bootstrapping

Tests for paired data

paired Prentice-Wilcoxon test

paired “t-test” for censored data

Day 2

Comparing Two Groups

Generalized Wilcoxon (nonparametric) test

MLE “t-test”

what to do with multiple reporting limits

Comparing Three or More Groups

Generalized Wilcoxon (nonparametric) test

MLE version of ANOVA

familiar tests for one reporting limit

Correlation Methods

censored correlation coefficients

what to do when one or both have multiple detection limits?

Kendall’s tau

likelihood correlation coefficient

Regression and Trends

how to compute a line with nondetects?

what to do with multiple reporting limits?

Akritas-Sen-Theil line

MLE for regression

logistic regression