Chapter 15
Mann-Whitney U Test

I. Assumptions

A. One independent variable

B. Two independent samples

C. Rank data

II. Combine the groups and rank the scores

A. Lowest score gets a rank of 1

B. Tied scores all get same rank

III. Separate the scores and sum the ranks

A. Sum the ranks for sample 1 ()

B. Sum the ranks for sample 2 ()

IV. Comput U₁and U₂

V. Check the computation of U₁and U₂

U₁ + U₂ = n₁ · n₂

VI. U is the smaller of U₁and U₂

VII. The Significance of U---(The rules are different for U)

A. Find the Critical Value from Table U

B. If U is < or = Critical Value, reject H_o

C. If U is > Critical Value, fail to reject H_o

Copyright © 1999, 2004 by Mark W. Vernoy