Compare 2 or more percentages

Contingency tables are a nonparametric procedure. No normality assumptions are required.

Are percentages in each category the same?
Nonparametric Approach. Contingency table test (or Test of Proportions). See chapter 14.

Are percentages in ordered categories (low, medium, high) the same?
Nonparametric Approach. Kruskal-Wallis test. See chapter 14.

Are percentages in ordered categories (10 years ago, 5 years ago, current) related to an ordered categorical response variable (low, medium, high)?
Nonparametric Approach. Kendall's tau correlation coefficient. See chapter 14.

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Chapter references are to the 2017 Second Edition of Statistical Methods in Water Resources.