Question

Cocoa and blood flow A study of blood flow involved $27$healthy people aged $18$to $72$. Each subject consumed a cocoa beverage containing $900$milligrams of flavonols daily for $5$days. Using a finger cuff, blood flow was measured on the first and fifth days of the study. After $5$ days, researchers measured what they called “significant 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 if the cocoa really caused the improved blood flow? Explain your answer.

Short answer

Irregularity in checkups makes it impossible to say if the cocoa really caused the improved blood flow.

Step-by-step solution

Given information

We are given that a study was conducted to check if the cocoa really caused the improved blood flow.

Simplify

Well, there is a flow in this study. Researcher's measured what they called “significant improvement” in blood flow and the function of the cells that line the blood vessels. as Flavanols, which are nutrients found in cocoa, are the active ingredient.
On cells, flavonols are thought to operate as antioxidants and anti-inflammatories.
But the flow is check up is done on the first and fifth days of the study , there can be so many circumstances that can have happened between five days. so it makes it impossible to say if the cocoa really caused the improved blood flow