Questions for Thought

  1. The average cost for rushed jobs is less than the average cost for those not rushed ($40.43 versus $38.59). Usually, having to do things in a hurry increases costs. Add the dummy variable D(Rush) to the stepwise model. Does the sign of the slope seem right now? How would you explain what’s happening? (Hint: look at Table 2.)

  2. The stepwise model (Table 6) includes the explanatory variable Sq. Temp Deviation, the square of the difference between room temperature and 75 degrees. Why 75? Add Room Temp itself to the regression, and then use the resulting estimates to find the optimal center for this quadratic effect.

  3. Suppose you initialize backward stepwise regression from the saturated model. Use Plant rather than Manager in ...

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