Case Series

• One kind of epidemiological study is known as a case series study. In this type of study, researchers follow the experience of a patient (or several patients with a similar diagnosis). This kind of study is usually more descriptive rather than statistically oriented and is not generally suited for making inferences about the general patient population with this diagnosis. Instead, these types of studies focus on unusual features of the patient and may be used to try and make new hypotheses about the disease. Data from this type of epidemiological study is then often used as a basis for other studies.
  
  

Case Control Studies

• Case control studies identify people based on whether or not they have a disease (their "disease status"). People with the disease are defined as the "case" group and people without it serve as the control. Ideally, the control group comes from the same population as the case group. These studies look in the past to try to identify factors (also known as "exposures") that lead to the development of the disease. Individuals are then divided up into four groups: exposed disease, unexposed disease, exposed control and unexposed control. This type of study can help identify the effects of genetics or other events, such as exposure to some potentially toxic agent, in the development of a disease within a population.
  
  

Cohort studies

• While case control studies look at a patient's medical history for insight, cohort studies look into the future. The "case" group in this case is a group of people that have been exposed to some risk factor for a disease (with the control group being unexposed), and the two groups are followed over time to look for the incidence of the disease. For example, non-smokers (control) and smokers (case) could be followed over time to see what percentage of them gets lung cancer, heart disease or any other number of possible outcomes. All patients in these studies should be initially free of the disease at the beginning of the study. This kind of study can also be used to help find a correlation between certain factors and disease development.