Nondetects And Data Analysis
For most environmental professionals, the way to deal with "nondetects" is less than obvious. Values below detection or reporting limits result from measuring trace amounts of a variety of organic and inorganic chemicals. This course presents up-to-date (maximum likelihood and survival analysis) methods for computing summary statistics, hypothesis tests, and regression for data with one or more detection limits. Example problems are worked in class, so students can confidently take these methods back to their office. The course assumes a knowledge of basic statistics, including some familiarity with t-tests, linear regression, and simple nonparametric tests like the rank-sum test.
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Textbook: Statistics for Censored Environmental Data Using Minitab and R
The second edition of Dennis Helsel's textbook for statistics with censored data
(published by Wiley, 2012) is available from your favorite bookseller. New in this edition are ✓
a chapter on multivariate methods for censored data, ✓
how to sum components of data with nondetects to obtain a total, and ✓
extensive use of methods that can incorporate values between detection and reporting limits ('remarked data').
Examples using R and Minitab are provided throughout the text.
Minitab macros for censored data
are available on our Downloads:NADA page
. Version 4.3 computes methods from the textbook using Minitab v.17. Available for free, as always.
R scripts for censored data
The NADA package for the R statistical software system is available from the CRAN site
Dennis Helsel (PhD in Environmental Science and Engineering, Virginia Tech) has over 32 years experience in applying statistical methods to environmental sciences. He has authored articles in numerous journals
, including papers on handling nondetect data such as “More Than Obvious” (ES&T 2005) and "Much Ado About Next to Nothing" (Ann. Occ. Hygiene, 2010). Dr. Helsel has authored Statistics for Censored Environmental Data using Minitab and R (Wiley, 2012), the textbook for this course, as well as Statistical Methods in Water Resources (USGS, 2002). Dr. Helsel is a 2003 recipient of the Distinguished Service Award from the American Statistical Association's section on Statistics and the Environment.Sign up for our newsletter
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