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On-Demand Webinars

Why Subbing One-Half of the Detection Limit is Trouble and
What you Can do Instead

Measurements of trace chemicals in environmental media (water, air, soils, biota) frequently result in values reported only as less than the laboratory reporting limit ("less-thans", "nondetects", and "qualified values"). The most commonly-used method for incorporating nondetects is to substitute one-half the reporting limit and continue as usual. This may obscure patterns and trends that are present, or may create those that are not present in the original data. It is fraught with error.

Two easily-implemented methods are available that avoid the problems with substitution. They can be used to compute summary statistics (mean, median), perform hypothesis tests, and compute regression models. The two methods incorporate data with one detection limit, or can be adapted to work with multiple detection limits.

Webinar Objectives and Highlights:

  • Why substituting one-half the detection limit causes problems
  • The effects of substitution on data
  • The effects of substitution on means, regression, hypothesis tests
  • Two easy methods that actually work with nondetect data

What You Will Learn:

  • You will be able to summarize (what's a typical value?) data with nondetects correctly.
  • You will no longer find trends and differences that are not really there (as substitution can do).
  • You will no longer miss trends and differences that ARE really there (as substitution can do).
  • You will know of easy methods for nondetects that actually work well.

Whether you want to learn more about statistical methods or managing detection limits, this webinar will provide participants with information that is not available elsewhere on the web.

Instructor Bio
Dennis Helsel, PhD
Author of Nondetects And Data Analysis: Statistics for Censored Environmental Data

Dennis Helsel, PhD has 32 years experience applying statistics to practical issues in environmental sciences. He is the owner and lead scientist of Practical Stats, an environmental statistics training and consulting firm. He is the lead author of two textbooks, Statistical Methods in Water Resources (USGS, 2002), and Nondetects And Data Analysis: Statistics for Censored Environmental Data (Wiley, 2005), as well chapters in two handbooks and over 50 journal articles.

Dr. Helsel was a 2003 recipient of the Distinguished Achievement Award from the American Statistical Association's section on Statistics and the Environment, and of the Dept. of Interior's Distinguished Service Award in 2007. He has been invited to conduct training classes on environmental statistics to the Chinese Ministry of Water Resources; to the Umweltbundesamt (German Environment Agency); to students at the Helsinki University of Technology, Finland; and in the United States through the American Statistical Association.

Fee: 299.00 USD Per Webinar

Downloads: Session Slides (PDF)
Record of Attendance Form (PDF)

Number of Participants: Unlimited from a single computer (Broadcast webinar in your conference room or auditorium for no extra charge)

Continuing Education Certificates: Unlimited. $14.95 each. Official CEU certificates are available as an option and only available at the time of webinar participation from Northern Illinois University. Ordering steps are given at time of webinar order.

Access: On-demand, anytime 24/7.
Access Duration: 24 hours.

Discounts: Buy 3 on-demand webinars, and get 3 on-demand webinars for free!

Duration: 90 minutes
PDH Earned: 1.5 hours
Instructor(s): Dennis Helsel, PhD
Author of Nondetects And Data Analysis: Statistics for Censored Environmental Data

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