The software outputs in Table 13.19 show results of fitting two models to data from a study of the relationship between y = percentage of adults voting, percentage of adults registered to vote, and racial–ethnic representation, for a random sample of 40 precincts in the state of Texas for a gubernatorial election. Racial–ethnic representation of a precinct is the group (Anglo, black, or Mexican American) having the strongest representation in a precinct.

(a) State a research question that could be addressed using these data.

(b) Report the prediction equation for the model assuming no interaction. Interpret the parameter estimates.

(c) Report the prediction equation for the model allowing interaction. Interpret the parameter estimates and describe the nature of the estimated interaction.

(d) Test whether the regression lines for the three categories have the same slope. Report the test statistic and P-value, and interpret.

(e) For the model assuming no interaction, test whether the mean voting percentages are equal for the three categories of racial–ethnic representation, controlling for percentage registered. Report the test statistic and P-value, and interpret.

(f ) Report the test statistic and P-value for testing the null hypothesis that percentage voting and percentage registered are independent, controlling for racial–ethnic representation.

Interpret.

(f) Summarize what you have learned about the question posed in

(a) from your analyses.