9. Refer to the previous exercise The means of percentage registered for the three categories are X = 762, X = 49.5. ;= 39.7, with an overall mean of X = 60.4

a) Find the adjusted means on percentage voting, and interpret.

b) Compare the adjusted mean for Auglos to the unadjusted mean of 52 3, and interpret

c) Sketch a plot of the no interaction model for these data. and identify on it the unadjusted and adjusted means

d) Using the appropriate model. test the null hypothesis that the true unadjusted means on percentage voting are equal Report the test statistic and P-value, and interpret Compare the result of this test to the one in Problem 13.8(f).

e) Describe how to expand the no interaction model to include the additional qualitative variable. location of precinct, with categories urban, suburban. small town, and rural. 1) Describe how to expand the no interaction model to include the additional quantitative explanatory variable. percentage of residents in precinct who are homeowners

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10 An analysis of covariance model is fitted to annual income (thousands of dollars), using predictors age and mantal status Table 13.19 shows the sample mean incomes and the adjusted means for the model. How could the adjusted means be so different from the unadjusted means Draw a sketch to help explain 11. Refer to Problem 13.1 The overall mean of father's education is 12 years Find the ad- justed mean educational levels for whites and nonwhites, controlling for father's educa- tion, and compare them to the unadjusted means. Concepts and Applications 12. Refer to the WWW data set (Problem 17). Using computer software, conduct and inter- pret an analysis of covariance using Y = political ideology. Prepare a report, presenting graphical, descriptive, and inferential analyses. using the predictors