The distribution center for an online retailer has been experiencing quite a few "pick errors" (i.e., retrieving the wrong item). Although the warehouse manager thinks most errors are due to inexperienced workers, she believes that a training program also may help to reduce them. Before sending all employees to training, she examines data from a pilot study of 30 employees (half attended training and the other half did not) to decide whether the training will be effective. A portion of the data is shown in the accompanying table.

Pick Errors (year to date).... Years of Experience.... Attended Training?(0=no, 1=yes)

13...................................................... 9.............................................. 0

3...................................................... 27.............................................. 0

⋮.......................................................................... ⋮............................................................... ⋮

4...................................................... 24 ..............................................1

a. Estimate two linear models:

Errors = β0 + β1 Exper + β2 Train + ε, and

Errors = β0 + β1 Exper + β2 Train + β3 Exper × Train + ε.

b. Using adjusted R2, summarize the fit results of the two models and specify which terms are significant at the 5% level. Which model is preferable in terms of fit?

c. Using the chosen model, by how much will pick errors be reduced, on average, for employees who attend the training program?

d. Use the chosen model to predict the number of pick errors for an employee with 10 years of experience who attended the training program, and for an employee with 20 years of experience who did not attend the training program.

e. Give a practical interpretation for the positive interaction coefficient.