Welcome to Practical Stats

For several decades Dennis Helsel as Practical Stats provided statistical training (in-person and online) and consulting for the environmental sciences and natural resources. Now that he has retired, he has made available here a number of resources for you to "Make Sense of Your Data" (our motto).

Training

Our Nondetects And Data Analysis training course is now available for free on our Training page. We're not aware that a similar course is available anywhere, whether free or not. It successfully trained students for years in statistical methods for data with nondetects. Learn how to compute everything from summary statistics to multivariate methods, all without substituting values like 1/2DL for nondetects.

Textbooks

1. Statistics for Censored Environmental Data (2nd edition) written by Dennis Helsel is the primary textbook in our Nondetects And Data Analysis training course. PDFs available as part of the course also provide examples of computing hypothesis tests, regression and more for censored (data with nondetects) data.

2. The 2020 version of the classic textbook Statistical Methods in Water Resources by Helsel and Hirsch is now available as
* a free download from the U.S. Geological Survey
* an inexpensive hardcopy sold by the US Geological Survey, at https://store.usgs.gov/product/533012

More information on both textbooks is found in our Books menu

Software

The NADA2 package for R provides advanced data analysis methods for censored data. It is now freely available at
https://cran.r-project.org/package=NADA2 . Hundreds of articles have used the procedures in NADA and NADA2 to evaluate their data without substituting fabricated values for nondetects. A list of only a few of these articles is on our NADA2 references page.

NADA2 goes well beyond estimating summary statistics in providing methods for data analysis of data with one or multiple detection limits. Without substituting any fraction of the detection limit(s), using NADA2 you can:
* Compute confidence, prediction and tolerance intervals
* Test for exceedances of a standard
* Perform matched pair (before/after, upstream/downstream, etc.) tests
* Test for group differences -- parametric, nonparametric and permutation tests
* Compute correlation coefficients and regression
* Draw QQ and partial plots to guide whether to transform x and y variables in regression
* Build multiple regression models and find models with the least error
* Perform parametric and nonparametric trend analyses
* Cluster groups of censored multivariate data
* Draw NMDS plots of censored multivariate data
* Test for group differences and trends of censored multivariate data
… .. and much more.

Videos

-- Recordings of webinars given by Dennis Helsel over the years. Our "𝝁Tube" for environmental statistics.
Available in the Videos menu are:
Videos for data analysis with nondetects (censored data)
Videos for general environmental statistics.

Privacy Policy

This site stores no cookies on your device. It does not track you in any way.
There are no advertisements unless YouTube places them into our videos (they are stored on YouTube).
Graphs only display the graphic, with no hidden functions.

Arrow to go to the top of the page