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, who wish to compare the baseline measures of systolic blood pressure across four different subgroups: non-smokers, current smokers, ex-smoker, and tobacco chewers. A sample is selected from each subgroup; the relevant data are shown below. Means and standard deviation are expressed in mm Hg. Assume that systolic blood pressure is normally distributed.

n x s

Non-smokers

Current smokers

Ex-smoker

Tobacco chewers

73 6.22 1.62

105 5.81 1.43

240 5.77 1.24

1080 5.47 1.31

(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 the significance, test the null hypothesis that the mean systolic blood pressures of the four groups are identical. What do you conclude?

Note:

To compute p-value use the following SAS codes:

Suppose observed F statistic value = x,

numerator df = k - 1 = d1 and

denominator df = n - k = d2 (where n is the total sample sizes in all three groups)

DATA prob;

p_value = 1 – PROBF(x, d1, d2); /*PROBF(x, d1, d2) returns cumulative probability, that is, P (F < x) */

RUN;

PROC PRINT; RUN;