In: Statistics and Probability
1. Here are the data from a small bookstore:
| 
 Number of Salespeople Working  | 
 Sales (in $1000s)  | 
| 
 2  | 
 10  | 
| 
 3  | 
 11  | 
| 
 7  | 
 13  | 
| 
 9  | 
 14  | 
| 
 10  | 
 18  | 
| 
 10  | 
 20  | 
| 
 12  | 
 20  | 
| 
 15  | 
 22  | 
| 
 16  | 
 22  | 
| 
 20  | 
 26  | 
a. Compute the correlation coefficient between number of salespeople and sales. Interpret the correlation coefficient. 6
b. Assuming the conditions for regression are met, find the estimated least-squares regression line and predicted sales on a day with 12 employees working. 7
c. If you expect the population regression coefficient to be positive, perform the hypothesis test of the regression coefficient at significance level of 0.05. 8
d. Find 95% prediction interval for Sales on a day with 12 employees working. 7
e. Comment on the overall quality of the fitted model using appropriate index. 7
a. Compute the correlation coefficient between number of salespeople and sales. Interpret the correlation coefficient
Sol:







the correlation coefficient between number of salespeople and sales is 0.9653.
b. Assuming the conditions for regression are met, find the estimated least-squares regression line and predicted sales on a day with 12 employees working
Sol:

The regression equaion is Y=8.1005+0.9134X
The predicted sales on a day with number of sales people
working
Y=8.10+0.913(12)
   =18.9