An observational study was used initially and then follow on questions remained for further study. The observational study 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. What type of study would be best to determine if flavonols were the cause of the increased blood flow?
An observational study with a survey where the participants are asked what foods they have eaten in the last 24 hours and their blood flow in
their skin is observed.
An experimental study where the study participants eat different foods and 2 different chocolates and their blood flow is monitored while they eat
them and afterwards. Afterwards, the blood flow returns to approximately the same value as before.
An experimental study where the participant blood flow is measured and then they eat dark chocolate and milk chocolate for a week and the
blood flow is measured again.