In Exercise 14.24 you probably noticed that many observations at Time 2 are missing. (This is partly because for many patients it had not yet been 3 months since the diagnosis.)

a. Compare the means at Time 1 for those subjects who did, and who did not, have data at Time 2.

b. If there are differences in (a), what would this suggest to you about the data?

In a study of behavior problems in children we asked 3 “judges” to rate each of 20 children on the level of aggressive behavior. These judges were the child’s Parent, the child’s Teacher, and the child him/herself (Self). The data follow.

Child 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Parent 10 12 14 8 16 21 10 15 18 6 22 14 19 22 11 14 18 25 22 7 Teacher 8 13 17 10 18 24 9 16 18 8 24 19 15 20 10 18 19 30 20 10 Self 12 17 16 15 24 24 13 17 21 13 29 23 16 20 15 17 21 25 25 14 These data are somewhat different from the data we saw in Section 14.10 because in that case the same people judged each child, whereas here the Parent and Self obviously change from child to child. We will ignore that for the moment and simply act as if we could somehow have the same parent and the same “self” do all the ratings.