Answer Problem 9.4 for two samples of size 12 and 15, with a rank sum of 220 in the sample of size 12. Assume there are no ties?

Suppose patients are graded on the degree of change in periodontal status on a 7-point scale, with +3 indicating the greatest improvement, 0 indicating no change, and −3 indicating the greatest decline. The data are given in Table 9.9.

Table 9.9: Degree of change in periodontal status

Change score ______________ Number of patients

+3 ………………………………………. 4

+2 ………………………………………. 5

+1 ………………………………………. 6

0 ………………………………………... 5

−1 ………………………………………. 4

−2 ………………………………………. 2

−3 ………………………………………. 2