Question

Chocolate gets my heart pumping Cardiologists at Athens Medical School in Greece wanted to test whether chocolate affected blood flow in the blood vessels. The researchers recruited $17$healthy young volunteers, who were each given a $3.5$-ounce bar of dark chocolate, either bittersweet or fake chocolate.

On another day, the volunteers were switched. The subjects had no chocolate outside the study, and investigators didn’t know whether a subject had eaten the real or the fake chocolate. An ultrasound was taken of each volunteer’s upper arm to see the functioning of the cells in the walls of the main artery. The investigators found that blood vessel function was improved when the subjects ate bittersweet chocolate, and that there were no such changes when they ate the placebo (fake chocolate).

(a) What type of design did the investigators use in their study?

(b) Explain why the investigators chose this design instead of a completely randomized design.

(c) Why is it important to randomly assign the order of the treatments for the subjects?

Short answer

(a) The design is matched pair design.

(b) This is because it uses same subjects in both groups that makes comparison easy for treatment as groups are identical.

(c) This is because it would be easy to recognize that the other chocolate is fake if first one is bittersweet chocolate.

Step-by-step solution

Given Information

Cardiologist wants to test if chocolates affect blood flow in blood vessels or not.

$17$healthy young recruiters were given $3.5$ ounce bar of chocolate either sweet or bitter. Ultrasound of upper arm is taken to check the functioning of blood cells.

To determine the type of design did the investigators use in their study.

Each volunteer underwent two treatments, bittersweet and fake. Hence, the experiment conducted is matched pair design experiment.

To explain why the investigators chose this design instead of a completely randomized design.

Matched pair design is used instead of a completely randomized design because completely randomized design results in two groups with no subject similar in both groups and each group will contain different subjects.

Matched pair design is easier for comparison for each comparison group as groups are identical.

To explain why is it important to randomly assign the order of the treatments for the subjects.

It is important to randomly assign the order of the treatments for the subjects because if all bittersweet chocolates are taken first by subject, they will recognize that the second one is fake.