6.6 Potthoff and Roy (1964) analyzed a longitudinal study of dental growth in children. Specifically, they measured the distance from the center of the pituitary gland to the maxillary fissure for children at ages 8, 10, 12, and 14. The data follow. Individual Girl 1 2 3 4 5 6 7 8 9 10 11 8 21 21 20.5 23.5 21.5 20 21.5 23 20 16.5 24.5 Age (in years) 10 20 21.5 24 24.5 23 21 22.5 23 21 19 25 12 21.5 24 24.5 25 22.5 21 23 23.5 22 19 28 14 23 25.5 26 26.5 23.5 22.5 25 24 21.5 19.5 28 Individual Boy 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 8 26 21.5 23 25.5 20 24.5 22 24 23 27.5 23 21.5 17 22.5 23 22 Age (in 10 25 22.5 22.5 27.5 23.5 25.5 22 21.5 20.5 28 23 23.5 24.5 25.5 24.5 21.5 i years) 12 29 23 24 26.5 22.5 27 24.5 24.5 31 31 23.5 24 26 25.5 26 23.5 14 31 26.5 27.5 27 26 28.5 26.5 25.5 26 31.5 25 28 29.5 26 30 25

(a) Perform a thorough analysis of these data assuming an exchangeable structure.

(b) Repeat part

(a) assuming an AR(1) structure.

(c) Repeat

(a) part using the robust approach.

(d) Compare and contrast the three analyses. Which seems most appropriate?