Question

Chocolate gets my heart pumping Cardiologists at Athens Medical School in Greece wanted to test if chocolate affects blood vessel function. 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 received the other treatment. The order in which subjects received the bittersweet and fake chocolate was determined at random. The subjects had no chocolate outside the study, and investigators didn't know if a subject had eaten the real or the fake chocolate. An ultrasound was taken of each volunteer's upper arm to observe the functioning of the cells in the walls of the main artery. The researchers 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 researchers use in their study?

b. Explain why the researchers 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?

d. Explain how and why researchers controlled for other variables in this experiment.

Short answer

(a) The matched pair design is used by researchers.

(b) The researchers chose this design instead of a completely randomized design because it results into two groups containing same subjects.

(c) It is important to randomly assign the order of the treatments because some people have bittersweet chocolate first and others get false chocolate first.

(d) The researchers controlled for other variables in this experiment by selecting young, healthy individuals.

Step-by-step solution

Part (a) Step 1: Given information 

We need to find the type of design did the researchers use in their study.

Part (a) Step 2: Explanation 

We know that

Each subject is administered for both treatments i.e. random order and comparison to themselves.

Therefore,

The matched pair design is used by researchers.

Part (b) Step 1: Given information 

We need to find the reason for researchers chose this design instead of a completely randomized design.

Part (b) Step 2: Explanation 

A completely randomized design will result in two groups being compared, neither of which will contain the same subjects. As a result, the groups will be distinct because each group will contain different subjects.

Because the subjects for both groups are the same, the outcomes for each treatment group will be easy to compare because the groups are identical.

Part (c) Step 1: Given information 

We need to find the importance of randomly assigning the order of the treatments.

Part (c) Step 2: Explanation 

We know that

Because if all of the subjects are given bittersweet chocolate first, they may notice that the second chocolate is fake.

As a result, it's preferable that some people have bittersweet chocolate first and others get false chocolate first.

Part (d) Step 1: Given information 

We need to find the way the researchers controlled for other variables in this experiment.

Part (d) Step 2: Explanation 

By selecting young, healthy individuals, the researchers were able to rule out any other potential health risks. They also made sure that no chocolate was consumed outside of the experiment's limits.

Other potential health conditions were ruled out because they could be to blame for the differences in blood vessel function between chocolate and non-chocolate. Outside chocolate eating was also monitored to guarantee that a placebo subject did not consume real chocolate and influence the results of the study.