The Mann-Whitney test can be performed on ordinal data. For example, a letter grade received in a class is ordinal data because it can be ranked: an A ranks higher than a B. A department chair wants to discover whether the grades of students in two different teachers' statistics courses are different. The chair randomly selects 15 students from professor A's class and 15 students from professor B's class and obtains the following data.

Do the following to test the belief that the grades administered in each class are equivalent.
(a) Rank the grades in descending order (A's first, then B's, and so on.)
(b) Perform a two-tailed test on the hypotheses
H0: the grades administered in each class are equivalent
H1: the grades administered in each class are different
by following Steps 1 through 5 (boxplots cannot be drawn).

Professor A D F Professor B B A A C D A A F A C B B