To test whether students in a higher grade level will be less disruptive in class, a school psychologist records the number of documented interruptions during one day of classes from nine local high schools. The sample consisted of nine (n = 9)

freshman, sophomore, junior, and senior high school classes. The data for each high school class are given in the table.

Freshman: 2, 4, 1, 5, 3, 1, 2, 0, 4

Sophomore: 4, 6, 0, 4, 3, 1, 1, 2, 0

Junior: 6, 0, 0, 4, 4, 6, 4, 5, 3

Senior: 3, 4, 3, 2, 2, 4, 2, 5, 4

Find the following:

1. Between groups: SS, df, MS, F
2. Within groups (error): SS, df, MF
3. Is it necessary to perform a post-hoc test? (assume alpha is equal to 0.05)