Gravetter/Wallnau/Forzano, Essentials - Chapter 4 - End-of-chapter question 38 A teacher is interested in the effect of a study session on quiz performance. Two different classes receive a pretest (before the study session) and a posttest (after the study session). Thus, the teacher records the following four sets of scores: Class 1 Pretest Class 1 Posttest 14 18 5 20 12 20 12 20 8 24 9 18 10 20 Class 2 Pretest Class 2 Posttest 20 10 2 21 12 12 8 28 12 21 4 20 12 28 For each of the four sets of scores above, calculate the sample mean (M) and standard deviation (s). Class 1 Class 2 Pretest M = M = s = s = Posttest M = M = s = s = The effect of the study session was most obvious in , in which the variability among scores was low. Any effect of study session in was obscured by the high variability among scores