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.

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!