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 scatterplot.
c. Compare the confidence intervals you calculated in parts c and d of Exercise 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 a = .05.

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