Correlation and Regression for Data with NDs
without substituting values for nondetects
Correlation and regression form the backbone of much of the data analysis in the environmental sciences. Computing coefficients, evaluating the quality of the regression and determining which variables produce the best equations are standard procedures. However, what can be done when data include values below detection or quantitation limits? This video will show you what is possible for these objectives, as well as for determining whether the methods’ assumptions are met (Q-Q plots) and to plot predicted values. You can do all of the tasks you are used to in correlation and regression, using parametric and nonparametric methods, all without substituting fabricated numbers for nondetects. This is just one topic from our online course Nondetects And Data Analysis.
Dennis Helsel (Ph.D. Environmental Science and Engineering):
"I'm a translator of statistical methods for scientists. My firm's name, Practical Stats, says it all. I've written/co-authored two textbooks. Statistics for Censored Environmental Data using Minitab and R (2012) pioneered statistical methods for data below detection limits. Statistical Methods in Water Resources (2020) has been cited by scientists throughout the world. I've taught webinars for the National Water Quality Monitoring Council and others; workshops for the American Statistical Association and others; courses such as AES and NADA for scientists in North America, Europe and Singapore since 1990. I worked for 30 years at the US Geological Survey before starting Practical Stats.
In 2003 I received the Distinguished Achievement Award from the American Statistical Association’s Section on Statistics and the Environment for my training courses in applied statistics.
In 2018 I received the Lifetime Achievement Award from the California Groundwater Resources Association for my communication of statistical methods to scientists. My courses provide up-to-date procedures communicated in clear language using video examples of data analysis of 'real data'."