(Data file: stopping) The (hypothetical) data in the file give automobile stopping Distance in feet and Speed in mph for n = 62 trials of various automobiles (Ezekiel and Fox, 1959).
Draw a scatterplot of Distance versus Speed. Explain why this graph supports fitting a quadratic regression model.
Fit the quadratic model but with constant variance. Compute the score test for non-constant variance for the alternatives that
(a) variance depends on the mean; (b) variance depends on Speed; and
(c) variance depends on Speed and Speed2. Is adding Speed2 helpful?
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