15.1 Tanning experiment Suppose the tanning experiment described in Examples 1 and 2 used only four participants, two for each treatment.

a. Show the six possible ways the four ranks could be allocated, two to each treatment, with no ties.

b. For each possible sample, find the mean rank for each treatment and the difference between the mean ranks.

c. Presuming H0 is true of identical treatment effects, construct the sampling distribution of the difference between the sample mean ranks for the two treatments.