A study of patients with insulindependent diabetes was condu

A study of patients with insulin-dependent diabetes was conducted to investigate the effects of cigarette smoking on 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: nonsmokers, current smokers, ex-smokers, and tobacco chewers. A sample is selected from each subgroup; the relevant data are shown in the table below. Means and standard deviations are expressed in mm Hg. Assume that systolic blood pressure is normally distributed.

n

x?

s

Nonsmokers

269

115

13.4

Current Smokers

53

114

10.1

Ex-smokers

28

118

11.6

Tobacco Chewers

9

126

12.2

a) Calculate the estimate of the within-groups variance.

b) Calculate the estimate of the between-groups variance.

c) At the 0.05 level of significance, test the null hypothesis that the mean systolic blood pressures of the four groups are identical. What do you conclude?

Solution