In an observational study, it was noticed that people that eat more chocolate tend to have better blood flow than the general population. Researchers wonder whether the improved blood flow might be...

In an observational study, it was noticed that people that eat more chocolate tend to have better blood flow than the general population. Researchers wonder whether the improved blood flow might be caused by flavanols (a molecule found in many foods). Dark chocolate contains a high concentration of flavanols, but milk chocolate contains a much lower concentration. How could the researchers design an experiment to determine the effects of flavanol on blood flow from the different types of chocolate?