9.10 Olejnik (1988) suggested that research studies in education and the social sciences should be concerned with differences in group variability as well as differences in group means. For example, a teacher can reduce variability in student achievement scores by focusing attention and classroom time on less able students. On the other hand, a teacher can increase variability in achievement by concentrating on the students with greatest ability and letting the less able students fall farther and farther behind. Previous research has indicated that mean student achievement for classes taught by teachers with a bachelor’s degree is not different from that of classes taught by teachers with a master’s degree. The present study was aimed at determining whether variability in student achievement is the same for these two teacher groups. The data below are the achievement scores on an examination (10¼highest possible score) given to two classes of 10 students. Class 1 was taught by a teacher with a master’s degree and class 2 by a teacher with a bachelor’s degree. The mean score is 5 for each class. Is there a difference in the variability of scores?
Class 1 Class 2 7 3 4 6 4 7 5 9 4 3 6 2 6 4 4 8 3 2 7 6