Mann-Whitney Test

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Calculate

Example: recovery time, in days, of patients on two treatments. There are few data and they don't look normal. Does one treatment recover faster? Change the values to work out your own case.

Group 1 Separated by spaces or commas. Group 2 The groups may have different sizes.

Step by step

What each term means

U Statistic: How many of the n₁ · n₂ comparisons between a value from group 1 and one from group 2 group 1 wins (ties count half). Near n₁n₂/2, the groups mix; near 0 or n₁n₂, one dominates the other.
Rank Sum (R₁): Pool the two groups, sort everything and add up the position of each value from group 1. Using positions makes the test immune to extreme values.
Smallest Possible Sum: The rank sum if group 1 had the n₁ smallest values: 1 + 2 + … + n₁. Subtracting it leaves only the wins over group 2.

When to use it, assumptions and alternatives: the Mann-Whitney U test in the statistical tests catalog.