The 2020 revision of the classic textbook Statistical Methods in Water Resources is now available as
* a free download from the U.S. Geological Survey
* an inexpensive hardcopy sold by the US Geological Survey, at

Many updates are present in the 2020 version of the textbook. Water resources data tend to have many variables with a lower bound of zero, tend to be more skewed than data from many other disciplines, and assumptions that the data are normally distributed are not appropriate. Computer-intensive methods (bootstrapping and permutation tests) now improve upon and replace the dependence on t-intervals, t-tests, and analysis of variance. A new chapter gives you principles to determine “How many observations do I need?” The chapter also presents distribution-free methods to help plan sampling efforts. The trends chapter has been updated to include the WRTDS (Weighted Regressions on Time, Discharge, and Season) method for analysis of water-quality data. New updated guidance on the use of statistical and graphical techniques are presented. The text utilizes R, a programming language and open-source software environment, for all exercises and most graphics, and the R code used to generate figures and examples is provided for download.

Chap 1. Summarizing Univariate Data
Chap 2. Graphical Data Analysis
Chap 3. Describing Uncertainty (interval estimates)
Chap 4. Hypothesis Tests
Chap 5. Testing Differences Between Two Independent Groups
Chap 6. Paired Difference Tests of the Center
Chap 7. Comparing Centers of Several Independent Groups
Chap 8. Correlation
Chap 9. Simple Linear Regression
Chap 10. Alternate Methods for Regression
Chap 11. Multiple Linear Regression
Chap 12. Trend Analysis
Chap 13. How Many Observations Do I Need?
Chap 14. Discrete Relations (contingency tables)
Chap 15. Regression for Discrete Responses (logistic regression)
Chap 16. Presentation Graphics

Reference as:
Helsel, D.R., Hirsch, R.M., Ryberg, K.R., Archfield, S.A., and Gilroy, E.J., 2020, Statistical Methods in Water Resources: U.S. Geological Survey Techniques and Methods, book 4, chapter A3, 458 p.
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