3 4 Linking research questions and methods Part 2
http://noang.org/
As you watch you will be able to draw a broad distinction between the observational and experimental (interventional) study designs.
In observational studies the investigator collects data on exposures associated with the occurrence, or progression, of an outcome without altering or manipulating the situation.
In interventional studies, the investigator changes something within the study population to understand its impact on the outcome.