In: Statistics and Probability
Question 2
In a study of the relationship between X = mean daily temperature for the month and Y = monthly charges on the electrical bill the following data was gathered:
| 
 Temperature (oF): Xi  | 
 16  | 
 28  | 
 13  | 
 22  | 
 25  | 
 19  | 
| 
 Number of Calls: Yi  | 
 95  | 
 120  | 
 70  | 
 115  | 
 130  | 
 85  | 
We are interested in fitting the following simple linear regression model: Y = Xβ + ε
a) Calculate X′X, (X′X)-1 and X′Y and then calculate the least squares estimates of β0 and β1.
b) Calculate the variance-covariance matrix of b, and use it to perform a t-test to test the null hypothesis that β1 = 0. Use α = 0.05.
Use the matrix approach to calculate the following:
c) Calculate a 95% confidence interval for the mean of Y when X = 20.
d) Calculate a 95% prediction interval for an individual new value of Y when X = 20.