Grocery retailer. A large, national grocery retailer tracks productivity and costs of its facilities closely. Data below were obtained from a single distribution center for a one-year period. Each data point for each variable represents one week of activity. The variables included are the number of cases shipped (X_I)' the indirect costs of the total labor hours as a percentage (X₂), a qualitative predictor called holiday that is coded 1 if the week has a holiday and 0 otherwise (X₃), and the total labor hours (Y).

a. Prepare separate stem-and-leaf plots for the number of cases shipped X_it and the indirect cost of the total hours X_i2. Are there any outlying cases present? Are there any gaps in the data?

b. The cases are given in consecutive weeks. Prepare a time plot for each predictor variable. - What do the plots show?

c. Obtain the scatter plot matrix and the correlation matrix. What information do these diagnostic aids provide here?