Comparing two groups
Welch, Student, paired and rank-based comparisons of two groups.
- Start here · Choose a methodWelch's t-test vs Student's t-test: which should you use?Use Welch's t-test by default to compare two independent groups. Here is why, how to check which test your software or AI assistant ran, and how to report it.
- Choose a methodPaired vs unpaired t-test: which one fits your experiment?Use a paired t-test when each value in one group has a partner in the other — the same animal measured twice, or matched samples. Here is how to tell, and what choosing wrongly does.
- Choose a methodMann–Whitney U test vs t-test: which should you use?The t-test compares means; the Mann–Whitney test asks whether one group tends to have larger values. Choose by the question you need answered, not by a normality test.
- Choose a methodCan you run a t-test with n = 3?Yes, a t-test works with three per group if each is an independent replicate — but it detects only large effects. Here is what n = 3 can tell you and how to use it well.
- Report a resultHow to report a t-test: templates for Welch, Student and paired testsCopy-ready sentences for reporting Welch's, Student's and paired t-tests in a paper, with what each number means and the details reviewers check first.
- Choose a methodHistopathology score statistics: ordinal scores, blinded scoring, fields within animals and which testCombine field or section scores into one score per animal, score blind, and compare animals with a Mann–Whitney test (or a t-test on mean field scores). Fields as n gave 41% false positives in simulation. Python and R code.