6.7 Thall and Vail (1990) compared a new treatment medication for epilepsy to a placebo. They recorded each patient's age and 8-week baseline seizure counts. They then monitored the 2-week seizure counts for each patient during four successive but nonoverlapping periods. The data follow. Perform a thorough analysis of these data. Is there a problem with overdispersion? Discuss the effect of the assumed correlation structure on your results.

Y\ Yi Yi YA Trt Base Age 5 3 2 4 7 5 6 40 5 14 26 12 4 7 16 11 0 37 3 3 3 3 2 8 18 2 3 13 11 8 0 3 3 5 4 4 18 2 4 20 6 13 12 6 4 9 24 0 0 29 5 0 4 4 3 12 24 1 1 15 14 7 4 6 3 3 0 1 9 8 0 23 6 6 6 8 6 12 10 0 3 28 2 6 3 3 3 2 76 2 4 13 9 9 3 1 3 3 5 4 21 7 2 12 5 0 22 4 2 14 9 5 3 29 5 7 4 4 5 8 25 1 2 12 8 4 0 3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 1 1 11 11 6 8 66 27 12 52 23 10 52 33 18 42 87 50 18 111 18 20 12 9 17 28 55 9 10 47 76 38 19 10 31 30 25 36 22 29 31 42 37 28 36 24 23 36 26 26 28 31 32 21 29 21 32 25 30 40 19 22 18 32 20 30 2 4 22 5 2 3 4 2 0 5 11 10 19 1 6 2 102 4 8 1 18 6 3 1 2 0 1 6 3 17 4 4 7 18 1 2 4 14 5 7 1 10 1 65 3 6 3 11 3 5 23 3 0 4 7 1 19 7 0 7 2 1 4 0 25 3 6 2 8 0 72 2 5 1 28 4 4 19 0 0 3 4 1 3 1 16 1 4 1 4 1 7 1 5 1 0 1 0 1 3 1 15 1 8 1 7 1 3 1 8 0 63 4 7 5 13 0 3 8 1 0 2 19 24 31 14 11 67 41 7 22 13 46 I 36 Í 38 I 1 I 36 I 11 I 151 I 22 I 41 I 32 I 56 I 24 I 16 I 22 I 25 I 13 1 12 18 24 30 35 27 20 22 28 23 40 33 21 35 25 26 25 22 32 25 35 21 41 32 26 21 36 37