Sample Covariance. For a set of n data points, the sample covariance, sxy, is given by sx y = (xi − x¯)(yi − y¯)

n − 1   

Defining formula

= xi yi − (xi)(yi)/n n − 1   

Computing formula

. (14.1)

The sample covariance can be used as an alternative method for finding the slope and y-intercept of a regression line. The formulas are b1 = sx y/s2 x and b0 = y¯ − b1x¯, (14.2)

where sx denotes the sample standard deviation of the x-values.

a. Use Equation (14.1) to determine the sample covariance of the data points in Exercise 14.45.

b. Use Equation (14.2) and your answer from part

(a) to find the regression equation. Compare your result to that found in Exercise 14.57.