Using the nonexperimental method, a researcher collects data on exercise and anxiety from a number of people and finds that exercise is negatively related to anxiety—that is, the people who exercise more tend to have lower levels of anxiety. What does this scenario demonstrate?

Co-variation between variables

Explanation:

Based on the scenario being described within the question it can be said that this scenario demonstrates the Co-variation between variables. This refers to the measure of how much two seemingly random variables vary together as opposed to separately which would otherwise be variance. Which explains why when one variable changes in value the other changes in an un-correlated way.

when an organism is covered by sediment, it begins to decay.