Rank correlation
Suppose a coach trains long-distance runners for one month using two methods.  Group A has 5 runners, and Group B has 4 runners.  The hypothesis is that method A produces faster runners.  The race to assess the results finds that the runners from Group A do indeed run faster, with the following ranks: 1, 2, 3, 4, and 6.  The slower runners from Group B thus have ranks of 5, 7, 8, and 9.