An educational psychologist studies the effect of frequent testing on retention of class material. In one of the professor's sections, students are given quizzes each week. The second section receives only two tests during the semester. At the end of the semester, both sections receive the same final exam, and the scores are summarized below.

a. Do the data indicate that testing frequency has a significant effect on performance? Use a two-tailed test with = .01.

b. Compute r² and state the size of the effect (e.g. small, medium, large).

Frequent Quizzes

n=15

M=72

SS=112

Two Exams

n=15

M=68

SS=98