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?

What is one major difference between an observational study and an experimental study?

Tyler is interested in how different environments affect dandelion plants. For a science fair project, Tyler looks for dandelions growing in the grass and growing in dirt without grass. He counts the number of days it takes each dandelion to turn from a yellow flower into seeds. After 6 weeks, he compares the results for the two groups.

1. What type of study is Tyler designing?
2. How could his design be improved to collect data that would be better for answering the question of interest?

For physics class, Jada wants to know how the surface of different ramps affects the maximum speed of a marble being rolled down the ramp. To study this, she compares the maximum speed of a marble rolled down ramps with different surfaces. She rolls the same marble down each type of ramp 10 times. What type of study is this?