It makes sense now to talk about multi-level models. This is definitely an advanced topic, and I'm not going to get into a whole lot of detail here. My objective right now is to introduce the concept of multi-level models to you, and let you understand some of the challenges and how to think about them when you're putting them together. That's it.
The concept of multi-level models is that some effects happen at various levels in the hierarchy. For example, your health. Your health might depend on how healthy your individual cells are, and those cells might be a function of how healthy the organs that they're inside are, and the health of your organs might depend on the health of you as a whole. Your health might depend in part on your family's health and the environment your family gives you. And your family's health in turn might...
