A randomized, controlled experiment investigated this question using a random sample of 540 adult males as subjects. At the begi
nning of the study, researchers measured the blood pressure of all the subjects. Each subject was given a month's supply of either Drug A, Drug B, or a placebo, then was assigned to be on either a low-fat diet or a low-salt diet for that month-long period. At the end of the month, the researchers measured the blood pressure of each subject again, and compared the two blood pressure readings. How many different groups are there altogether in this study?
You have 3 possible supplies for each subject and they can have 2 different king of diets. That gives you alredy 3*2 = 6 different options to study. You can divide further when you make the comparisson at the end of the month, allowing you to subdivide into two more categories: wheater their blood pressure is higher or lower.
That gives you a total of 3*2*2 = 12 groups to study.
