a. Compute the standard deviation for the pretest and posttest scores that were used in problems 2.6 and 3.12. The scores are reproduced here.

Taking into account all of the information SOC you have on these variables, write a paragraph describing how the sample changed from test to test. What does the standard deviation add to the information you already had?

Case Pretest Posttest A 8 12 B 7 13 C 10 12 D 15 19 E 10 8 F 10 17 G 3 12 H 10 11 I 57 J 15 12 K 13 20 L45 M 10 15 N 8 11 O 12 20

b. Frequency distributions for both pretest and posttest scores are presented here. Use this information to compute a mean and standard deviation for each group, and compare these values with the actual mean and standard deviation you computed earlier. How accurate are the approximate mean and standard deviation as compared to the actual statistics?

Pretest Scores Frequency (f )

0–4 2 5–9 4 10–14 7 15–19 2 20–24 0 N
15 Posttest Scores Frequency (f )

0–4 0 5–9 3 10–14 7 15–19 3 20–24 2 N
15