The depth of wetting of a soil is the depth to which water content will increase owing to external factors. The article €œDiscussion of Method for Evaluation of Depth of Wetting in Residential Areas€ (J. Nelson, K. Chao, and D. Overton, Journal of Geotechnical and Geoenvironmental Engineering, 2011:293€“296) discusses the relationship between depth of wetting beneath a structure and the age of the structure. The article presents measurements of depth of wetting, in meters, and the ages, in years, of 21 houses, as shown in the following table.

a. Compute the least-squares line for predicting depth of wetting (y) from age (x).

b. Identify a point with an unusually large x-value. Compute the least-squares line that results from deletion of this point.

c. Identify another point which can be classified as an outlier. Compute the least-squares line that results from deletion of the outlier, replacing the point with the unusually large x-value.

d. Which of these two points is more influential? Explain.    

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Age Depth Depth Age 3 7.6 4 5.5 4 4.6 3 6.1 10.7 6.1 9.1 10.4 3 4.3 4 4.6 7.3 5.2 10.4 15.5 7.0 6.1 14 16.8 10 9.1 5.8 8.8 10.7