Water Resources of the United States

# NADA for R: Nondetects and Data Analysis for the R
statistical computing environment

## Description:

NADA for R is a library package for the R environment for
graphics and statistics. The package contains data and analysis
methods described in the book Nondetects and Data Analysis:
Statistics for Censored Environmental Data , Helsel (2005) -- See
references below.

NADA for R can be used to plot data, generate summary
statistics, compute exceedance probabilities, and perform
hypothesis tests, on data containing multiple censoring
thresholds (a.k.a nondetects, or less-thans).

All functions within NADA for R are presented within a clear,
consistent, and easy to use framework.

## Contents:

- Statistical Methods
- Robust Regression on Order Statistics (Robust ROS)
- Empirical cumulative distribution functions (ECDFs)
using Kaplan-Meier methods
- Nonparametric hypothesis testing based on ECDFs and
rank-sum methods.
- Maximum Likelihood Estimation summary statistic, and
regression methods.
- Censored probability plots
- Censored boxplots

- Miscellaneous
- Generic summary, printing, and plotting functions.
- All statistical methods have common query and
prediction functions that allow the computation of summary
statistics and prediction of modeled values.

## References:

Dennis R. Helsel, 2005. Nondetects and Data Analysis:
Statistics for Censored Environmental Data. John Wiley and Sons,
New York, 250p.

Lopaka Lee and Dennis Helsel, 2005. Statistical analysis of
water-quality data containing multiple detection limits I:
S-language software for regression on order statistics. Computers
and Geoscience, 31, 1241-1248.

Lopaka Lee and Dennis Helsel, 2005. Baseline Models of Trace
Elements in Major Aquifers of the United States. Applied
Geochemistry, 20, 1560-1570.

Lopaka Lee and Dennis Helsel, (in press) Statistical analysis
of water-quality data containing multiple detection limits II:
S-language software for nonparametric distribution modeling and
hypothesis testing. Computers and Geoscience.

## Installing NADA for R:

The primary requirement for running the software is a working
installation of the R environment. R can be obtained at
http://www.r-project.org/.

Once R is installed and the machine has a functioning internet
connection, the NADA package may be automatically installed using
the following command:

> install.packages("NADA")

Both R and NADA for R are Free Software and can be obtained,
used, modified and distributed under the terms of the GNU General
Public License (version 2 or newer).