The data in Table 11.20 concern the growth of pines in Colorado. The variables for a set of randomly sampled trees are: RINGS: the number of rings, which is the age of the tree, CIRCUM: the circumference of the tree at four feet, and SIDE: the side of the mountain on which the tree is found: NORTH: the north slope, SOUTH: the south slope.
We want to establish the relationship of tree size to age and determine how that relationship may be affected by the side on which the tree is located.
(a) Perform an analysis of covariance for CIRCUM using SIDE as the factor and RINGS as the covariate. Interpret results as they apply to the questions asked.
(b) Perform a test to see whether the relationship of RINGS to CIRCUM is different for the two sides of the mountain. How do these results change the interpretations in part (a)?
(c) Define GROWTH as the ratio (CIRCUM)/(RINGS). What does this variable mean and how can it be used to answer the questions posed in the problem statement?
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