In: Statistics and Probability
A sales manager collected the following data on annual sales for new customer accounts and the number of years of experience for a sample of salespersons. Salesperson Years of Experience Annual Sales ($1000s)
1 1 80
2 2 100
3 3 106
4 4 105
5 6 111
6 8 120
7 9 121
8 11 116
9 13 136
10 14 142
The data y= on annual sales($1000s) for new customer accounts and x= number of years of experience for a sample of 10 salespersons provided the estimated regression equation y=88.22+3.59x . For these data x=7.1, (xi-x)2192.90 , and s=6.8693.
a. Develop the 95% confidence interval for the mean annual sales for all salespersons with twelve years of experience. ( , ) (to 2 decimals)
b. The company is considering hiring Tom Smart, a salesperson with twelve years of experience. Develop a 95% prediction interval of annual sales for Tom Smart. ( , ) (to 2 decimals)
Solution: We can use the excel regression data analysis tool to find the answers to the given questions. The excel output is given below:
| Regression Analysis | ||||||
| Regression Statistics | ||||||
| Multiple R | 0.9317 | |||||
| R Square | 0.8681 | |||||
| Adjusted R Square | 0.8516 | |||||
| Standard Error | 6.8693 | |||||
| Observations | 10 | |||||
| ANOVA | ||||||
| df | SS | MS | F | Significance F | ||
| Regression | 1 | 2484.5997 | 2484.5997 | 52.6537 | 0.0001 | |
| Residual | 8 | 377.5003 | 47.1875 | |||
| Total | 9 | 2862.1 | ||||
| Coefficients | Standard Error | t Stat | P-value | Lower 95% | Upper 95% | |
| Intercept | 88.21877 | 4.12918 | 21.36471 | 0.00000 | 78.69686 | 97.74067 | 
| Years of Experience | 3.58891 | 0.49459 | 7.25629 | 0.00009 | 2.44837 | 4.72944 | 
| For Average Y | ||||||
| Interval Half-Width | 7.51 | |||||
| Confidence Interval Lower Limit | 123.78 | |||||
| Confidence Interval Upper Limit | 138.79 | |||||
| For Individual Response Y | ||||||
| Interval Half-Width | 17.53 | |||||
| Prediction Interval Lower Limit | 113.76 | |||||
| Prediction Interval Upper Limit | 148.81 | |||||
a. Develop the 95% confidence interval for the mean annual sales for all salespersons with twelve years of experience. ( , ) (to 2 decimals)
Answer: 
b. The company is considering hiring Tom Smart, a salesperson with twelve years of experience. Develop a 95% prediction interval of annual sales for Tom Smart. ( , ) (to 2 decimals)
Answer: