# solution

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. Refer to the online stock brokerage data in Exercise 11.23 (page 589). Plot assets versus the number of accounts. Investigate the possibility that the relationship is curved by running a multiple regression to predict assets using the number of accounts and the square of the number of accounts as explanatory variables. (Note that to use statistical inference for these data, we need to assume that there is some underlying model that generated the data and that it is the properties of this model that are of interest.) DATADATA

DATA FILE

BROKERAGE

(a) Give the fitted regression equation.

(b) Find a 95% confidence interval for the coefficient of the squared term.

(c) Give the results of the significance test for the coefficient ofthe squared term. Report the test statistic with its degrees of freedom and P-value, and summarize your conclusion.

(d) Rerun the analysis without the quadratic term. Explain why the coefficient of the number of accounts is not the same as you

found for part (a).

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