4.A study of patient 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 below.Means and standard deviations are expressed in mmHg.Assume that systolic blood pressure is normally distributed.Test the null hypothesis that the mean systolic blood pressures of the four groups are identical.

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