Epidemiologic studies are divided into the two major areas: observational and experimental.  Observational studies are usually called either descriptive or analytical.  If one plans to conduct an observational study, one does not have control over the study subjects.  The researcher simply observes the outcome and factors associated with the disease.    On the other hand, an experimental study has full control over the study subjects.  This type of study is usually conducted in a clinical, community intervention, and field trial setting.  I will be discussing about each study in the latter part of my lecture.