Studies in which data is gathered from participants without manipulation by the researchers, such as through interviews. May sometimes be the only ethical option for a study. Do not necessarily prove casual relationships, only provide associations to suggest possible causes

Observational Studies

Studies in which investigators manipulate the participants to find associations as well as causation; Provide strong evidence for cause/etiology, but must be carefully assessed for bias

Experimental Studies

Types of epidemiological studies include:

- Observational studies
- Experimental studies

University of Notre Dame

Regarding epidemiology, the expectation is that analyzing the distribution of cases in a community or region and uncovering the distinguishing characteristics of the affected individuals or groups will teach us something about the causes of a particular disease and the methods by which it spreads. Epidemiological methods can also be quite important in identifying groups of individuals who are at risk.

Epidemiological Methods 

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- analyzing the distribution of cases in a community or region and uncovering the distinguishing characteristics of the affected individuals or groups
- Epidemiological methods can also be quite important in identifying groups of individuals who are at risk.

Expectations for Epidemiological Methods

The study Smoking and Health (Surgeon General, 1964). 
- This study linked cigarette smoking with lung cancer by the simple methods of counting and correlating.
- There were definite relationships and associations between smoking and lung cancer (e.g., about 90% of lung cancer in males was associated with cigarette smoking, and the amount and duration of smoking were positively correlated with probability of cancer).
- It is true that epidemiological research frequently suggests the possibility of multiple causation (several factors must be present before the disease occurs, or the greater the number associated factors that are present, the greater the risk of the disease). 

Smoking and Health Study

Much of epidemiological research is based on interview and surveys. Survey and interview data present a number of issues and potential problems. we need objective methods of defining and measuring a problem. Further, we need survey procedures that will enable us to estimate the problem's true incidence or prevalence and not just to locate 
those cases that are already under treatment or that have identified themselves by seeking treatment

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