In: Statistics and Probability
A. Jensen Tire & Auto is in the process of deciding whether to purchase a maintenance contract for its new computer wheel alignment and balancing machine. Managers feel that maintenance expense should be related to usage, and they collected the following information on weekly usage (hours) and annual maintenance expense (in hundreds of dollars): Weekly Usage (hours) Annual Maintenance Expense ($100) 13 17.0 20 30.0 28 37.0 32 47.0 17 30.5 24 32.5 40 51.5 38 40.0 A2. Using the OLS results and find the predicted value of yi, i.e., , that corresponds with 32 hours of weekly usage of this machine: a. 37.2004 b. 41.2348 c. 33.1660 d. 47.2865 A5. Find sy.x (=sɛ) (standard error of the model): a. 137.4193 b. 4.7857 c. 26.9705 d. 8.9594 A6. Find the 99% confidence interval for β1: a. (0.5555, 1.4617) b. (1.4617, 0.3221) c. (0.3221, 1.6951) d. (0.5555, 1.6951) A7. Using a 5% level of significance, is the effect of “Weekly Usage” on “Annual Maintenance Expense”: a. positively and significantly b. positively and insignificantly c. negatively and significantly d. negatively and insignificantly
Solution: We can use the excel regression data analysis tool to find the answer to the given questions. The excel output is given below:
SUMMARY OUTPUT | ||||||
Regression Statistics | ||||||
Multiple R | 0.9120 | |||||
R Square | 0.8318 | |||||
Adjusted R Square | 0.8038 | |||||
Standard Error | 4.7857 | |||||
Observations | 8 | |||||
ANOVA | ||||||
df | SS | MS | F | Significance F | ||
Regression | 1 | 679.5494948 | 679.5494948 | 29.6704924 | 0.001591769 | |
Residual | 6 | 137.4192552 | 22.90320921 | |||
Total | 7 | 816.96875 | ||||
Coefficients | Standard Error | t Stat | P-value | Lower 99.0% | Upper 99.0% | |
Intercept | 8.9594 | 5.1904 | 1.7261 | 0.1351 | -10.2837 | 28.2025 |
x | 1.0086 | 0.1852 | 5.4471 | 0.0016 | 0.3221 | 1.6951 |
Using the OLS results and find the predicted value of yi, i.e., , that corresponds with 32 hours of weekly usage of this machine:
Answer: b. 41.2348
Explanation:
The regression equation is:
Find sy.x (=sɛ) (standard error of the model):
Answer: b. 4.7857
Find the 99% confidence interval for β1:
Answer: c. (0.3221, 1.6951)
Using a 5% level of significance is the effect of “Weekly Usage” on “Annual Maintenance Expense”:
Answer: a. positively and significantly