In a production facility, an accurate estimate of manhours needed to complete a task is crucial to manage ment in making such decisions as the proper number of workers to hire, an accurate deadline to quote a client, or cost-analysis decisions regarding budgets. A manufacturer of boiler drums wants to use regression to predict the number of man-hours needed to erect the drums in future projects. To accomplish this, data for 35 boilers were collected. In addition to man-hours (y), the variables measured were boiler capacity (x, = Iblhr), boiler design pressure (x2 = pounds per square inch or psi), boiler type (x, = 1 if industry field erected, 0 if utility field erected), and drum type (x, = 1 if steam, 0 if mud). The data are provided in the table on page 598. A MINITAB printout for the model E(y) =PO + PIXI +P2~2 + P3x3 + P4~4 is shown on page 597.

a. Conduct a test for the global utility of the model.
Use a = .01.

b. Both a 95% confidence interval for E(y) and a 95%
prediction interval for y when xl = 150,000, x2 = 500, x3 = 1 and x, = 0 are shown at the bottom of the MINITAB printout. Interpret both of these intervals.