Choosing a test for two samples

Start from the data type and the design, not from the software menu.

• Means, independent groups: Welch's t-test by default.
• Means, paired measurements: paired t-test on differences.
• Ordinal or heavy-tailed data: Mann–Whitney or Wilcoxon signed-rank.
• Proportions: two-proportion z-test, Fisher's exact test for small counts.

Always report the estimate with an interval, not only the p-value.

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