Wilcoxon rank sum test

(aka Mann-Whitney U test)

• Non-parametric equivalent of parametric t-test for
  2 independent samples (unpaired t-test)


• Suppose the waiting time (in days) for cataract
  surgery at two eye clinics are as follows:

Patients at clinic A

(nA=18)

1, 5, 15, 7, 42, 13, 8, 35, 21,

12, 12, 22, 3, 14, 4, 2, 7, 2

Patients at clinic B

(nB=15)

4, 9, 6, 2, 10, 11, 16, 18, 6, 0,

9, 11, 7, 11, 10