Refer to Exercise 11.77.
a. Using no information about x, estimate and calculate a 95% confidence interval for the mean value of y.
b. Plot the estimated mean value and the confidence interval as horizontal lines on your scatter plot.
c. Compare the confidence intervals you calculated in parts c and d of Exercise 11.77 with the one you calculated in part a of this exercise. Does x appear to contribute information about the mean value of y?
d. Check the answer you gave in part c with a statistical test of the null hypothesis H0: β1 = 0 against Ha: β1 ‰  0. Use α = .05.
Exercise 11.77
Consider the pairs of measurements shown in the table. For these data, SSxx = 38.9, SSyy = 33.6, SSxy = 32.8, and = -.414 + .843x.

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