A study of patients with insulin-dependent diabetes was conducted to investigate the effects of cigarette smoking in renal and retinal complications. Before examining the results of the study, you wish to compare the baseline measures of systolic blood pressure across four different subgroups: nonsmoker, current smokers, ex-smokers, and tobacco chewers. A sample is selected from each subgroup; the relevant data is shown below. Means and standard deviation are expressed in mm Hg. Assume the systolic blood pressure is normally distributed. In order of n, xbar, and s, the results are the following:
n xbar s
Nonsmokers 269 115 13.4
Current Smokers 52 114 10.1
Ex-smokers 28 118 11.6
Tobacco chewers 9 126 12.2
a) Compute the estimate of the within-groups variance.+
b) Compute the estimate of the between-groups variance.
c) At the 0.05 level of significance, test the null hypothesis that mean systolic blood pressures of the four groups are identical. What do you conclude?
d) If you find the population means are not all equal, use the Bonferroni multiple comparisons procedure to determine where the differences lie. What is the significance level of each individual test?