Professor Brunner had students in his Marketing class rate his performance as Excellent, Good, Fair, or Poor. A graduate student collected the ratings and assured the students that Professor Brunner would not receive them until after the course grades had been submitted. The rating (the treatment) a student gave the professor was matched with his/her course grade, which could range from 0 to 100. the data is as follows:
Excellent Good Fair Poor
94 75 70 68
90 68 73 70
85 77 76 72
80 83 78 65
88 80 74
68 65
65
Is there a difference in the mean scores of the students in each of the four rating categories at a 99% confidence level?