Estimating repair and replacement costs of water pipes. Refer to the IHS Journal of Hydraulic Engineering (September 2012) study of water pipes, Exercise 11.12 (p. 650). Recall that a team of civil engineers used regression analysis to estimate y = the ratio of repair to replacement cost of commercial pipe. The independent variable in the regression analysis was x = the diameter (in millimeters) of the pipe. Data for a sample of 13 different pipe sizes are provided in the table below, followed by a Minitab simple linear regression printout on the next page. Diameter (mm) Ratio 80 6.58 100 6.97 125 7.39 150 7.61 200 7.78 250 7.92 300 8.20 350 8.42 400 8.60 450 8.97 500 9.31 600 9.47 700 9.72 Source: Based on ISH Journal of Hydraulic Engineering, Volume 18, Issue 3, pp. 241–251. Copyright: September 2012.

a. Find the least squares line relating ratio of repair to replacement cost (y) to pipe diameter (x) on the printout.

b. Locate the value of SSE on the printout. Is there another line with an average error of 0 that has a smaller SSE than the line, part a? Explain.

c. Interpret, practically, the values bn 0 and bn 1 .

d. Use the regression line to predict the ratio of repair to replacement cost of pipe with a diameter of 800 millimeters.

e. Comment on the reliability of the prediction, part d.