two different species, or people from two separate cities), perform a two-sample t-test (a.k.a.
If the groups come from two different populations (e.g. measuring before and after an experimental treatment), perform a paired t-test. If the groups come from a single population (e.g. One-sample, two-sample, or paired t-test? When choosing a t-test, you will need to consider two things: whether the groups being compared come from a single population or two different populations, and whether you want to test the difference in a specific direction. If your data do not fit these assumptions, you can try a nonparametric alternative to the t-test, such as the Wilcoxon Signed-Rank test for data with unequal variances. have a similar amount of variance within each group being compared (a.k.a. are (approximately) normally distributed. The t-test is a parametric test of difference, meaning that it makes the same assumptions about your data as other parametric tests. 
If you want to compare more than two groups, or if you want to do multiple pairwise comparisons, use an ANOVA test or a post-hoc test. Frequently asked questions about t-testsĪ t-test can only be used when comparing the means of two groups (a.k.a.
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