Bridge tour. Refer to the data concerning the heights of the bridges (in meters) and main span length (in meters) in China, Exercise 11.39 (p. 666). Recall that you have evaluated the straight-line model relating the main span length (y) to the height (x) of the bridges.

a. Refer back to the output printout of the analysis for the above. Is the model statistically useful for predicting y? Test using a = .01.

b. A portion of the output printout giving a 95% confidence interval for E1y2 and a 95% prediction interval for y when x = 300 is shown below. Interpret both intervals practically. Which interval should be used to predict the main span length of a bridge with height 300? Regression Equation SpanL = -272.6654 + 2.6817 Height Settings Variables Setting Height 300 Prediction Fit SE Fit 95% CI 95% PI 531.852 233.371 (485.845, 577.860) (67.388, 996.317)