Question

Cocoa and blood flowA study conducted by Norman Hollenberg, professor of medicine at Brigham and Women’s Hospital and Harvard Medical School,

involved $27$healthy people aged $18-72$. Each subject consumed a cocoa beverage containing $900$milligrams of flavonols (a class of flavonoids) daily

for five days. Using a finger cuff, blood flow was measured on the first and fifth days of the study. After five days, researchers measured what they called “signifi-

cant improvement” in blood flow and the function of the cells that line the blood vessels. What flaw in the design of this experiment makes it impossible to say

whether the cocoa really caused the improved blood flow? Explain.

Short answer

There is no group that was treated or received placebo care.

Step-by-step solution

Given Information

Twenty seven healthy people aged between $18-72$consumed $900$milligrams of flavonols for five days. Blood flow was measured on the first and fifth days of the study.

After five days, researchers measured what they called “significant improvement” in blood flow and the function of the cells that line the blood vessels.

Simplification

There is no monitoring group for comparison.

The primary aim of test group is to create a benchmark for comparison of impacts of other treatments. It is not clear that whether it was a placebo or flavonols directly affecting flow of blood. Cocoa could not tell induction of increased blood flow.