Does increasing calcium intake reduce blood pressure? Observational studies suggest that there is a link, and that it is strongest in African-American men. Twenty-one African-American men participated in an experiment to test this hypothesis. Ten of the men took a calcium supplement for 12 weeks while the remaining 11 men recieved a placebo. Researchers measured the blood pressure of each subject before and after the 12-week period. The experiment was double-blind.
A pooled t-test is appropriate for comparing the change in blood pressure between the treatment and placebo groups. Normal probability plots of blood pressure change for the two groups do not show problematic departures from normality, and the sample standard deviations do not rule out equal population standard deviations. The pooled t-statistic is 1.634, with a p-value of .059.
A two-sample t-test or one-way ANOVA may also be used to analyze these data.