A psychology class performed an experiment to determine whether a recall score in which instructions to form images of 25 words were given differs from an initial recall score for which no imagery instructions were given. Twenty students participated in the experiment with the results listed in the table.

a. What three testing procedures can be used to test for differences in the distribution of recall scores with and without imagery? What assumptions are required for the parametric procedure? Do these data satisfy these assumptions?
b. Use both the sign test and the Wilcoxon signed rank test to test for differences in the distributions of recall scores under these two conditions.

Without With Without Student Imagery Imagery Student Imagery Imagery With 24 20 18 12 13 20 20 16 24 16 12 16 25 21 19 19 18 10 20 13