Question: The American Time Use Survey of 2003 stated that the average American consumes 31 pounds of cheese in a year. A reporter speculated that Americans' love of cheese may play a role in the fact that they're getting heavier. If an observational study showed that the more cheese you eat, the more you weigh, can it be concluded that cheese in particular makes you gain weight? Could the theory be tested with an experiment instead of with an observational study?