Question: Blood pressure. A randomized comparative experiment studied the effect of diet on blood pressure. Researchers divided 54 healthy white males at random into two groups. One group received a calcium supplement; the other, a placebo. At the beginning of the study, the researchers measured many variables on the subjects. The paper reporting the study gives x¯ = 114.9 and s = 9.3 for the seated systolic blood pressure of the 27 members of the placebo group.
(a) Give a 95% confidence interval for the mean blood pressure of the population from which the subjects were recruited.
(b) The recipe you used in part (a) requires an important assumption about the 27 men who provided the data. What is this assumption?