Describe each type and give an example of when these type of investigations/studies are used

Epidemiologists conduct investigations to better understand how disease is distributed in the population and what determines who gets sick and who does not.

1. Name 2 types of studies conducted by Epidemiologists.
2. Describe each type and give an example of when these type of investigations/studies are used
3. Describe in your own works Criteria of Causation and how it relates to exposure and a suspected risk factor
Please list and compare several of the differences.