Compare 3 or more groups
Do the centers of two
groups differ?
Parametric Approach: Two-sample t-test.
Tests differences in means. Assumes normal distribution in
both groups. See chap. 5.
Nonparametric Approach. Rank-sum (also
called Mann-Whitney) test. Tests differences in medians. No
distributional assumption required. See chap. 5.
Do paired data differ?
Parametric Approach: Paired t-test. Tests
whether the mean difference is zero. Assumes differences
follow a normal distribution. See chapter 6.
Nonparametric Approach. Sign or
signed-rank test. Tests whether the median difference is
zero. No assumption of a normal distribution required. See
chapter 6.
Do the centers of three or
more groups differ?
Parametric Approach: Analysis of variance.
Tests differences between means. Assumes residuals follow a
normal distribution. See chapter 7.
Nonparametric Approach. Kruskal-Wallis
test. Tests differences between medians. Does not require
data follow a normal distribution. See chapter 7.
Chapter references are to the course textbook Statistical Methods in Water
Resources.