Chapter 8.3, Problem 18E

The article “Models for Assessing Hoisting Times of Tower Cranes” (A. Leung and C. Tam, Journal of Construction Engineering and Management, 1999: 385–391) presents a model constructed by a stepwise regression procedure to predict the time needed for a tower crane hoisting operation. Twenty variables were considered, and the stepwise procedure chose a nine-variable model. The adjusted R² for the selected model was 0.73. True or false:

1. a. The value 0.73 is a reliable measure of the goodness of fit of the selected model.
2. b. The value 0.73 may exaggerate the goodness of fit of the model.
3. c. A stepwise regression procedure selects only variables that are of some use in predicting the value of the dependent variable.
4. d. It is possible for a variable that is of no use in predicting the value of a dependent variable to be part of a model selected by a stepwise regression procedure.