In Exercise 8.2-13, data are given that show the effect of a certain fertilizer on plant growth. The growths of the plants in mm over six weeks are repeated here, where Group A received fertilizer and Group B did not:

We shall test the hypothesis that fertilizer enhanced the growth of the plants.
(a) Construct a back-to-back stem-and-leaf display in which the stems are put down the center of the diagram and the Group A leaves go to the left while the Group B leaves go to the right.
(b) Calculate the value of the Wilcoxon statistic and give your conclusion.
(c) How does this result compare with that using the t test in Exercise 8.2-13?

Group A: 55 61 33 57 17 46 50 42 71 51 63 Group B: 31 27 12 44 9 25 34 53 33 21 32