Problem 8 in Chapter 12 involved comparing straight-line regression fits of SBP on QUET for smokers and nonsmokers, and it was found that these straight lines could be considered parallel. Use results based on that problem and the computer output given next (and the fact that the overall sample mean value QUET = 3.441) to address the following issues.
a. State the appropriate ANACOVA regression model to use for comparing the mean blood pressures in the two smoking categories, controlling for QUET.
b. Determine the adjusted SBP means for smokers and nonsmokers. Compare these values to the unadjusted mean values
SBP(smokers) = 147.823 and SBP( nonsmokers) = 140.800
c. Test whether the true adjusted mean blood pressures in the two groups are equal. State the null hypothesis in terms of the regression coefficients in the ANACOVA model given in part (a).
d. Obtain a 95% confidence interval for the true difference in adjusted SBP means.