In epidemiology, the study mainly deals only with the distribution of diseases/conditions in humans and with the factors influencing the distribution and the frequency of diseases. Study design can be mainly classified into two types,
Observational study design and Experimental study design.
The reason to conduct studies is:
- To describe the burden, severity, prevalence of the disease, risk factors, and health behaviors that increase the risk of disease.
- To determine how effective the intervention is.
Observational Studies: In these types of study the investigator observes the occurrence of the disease in population groups that are exposed to some exposure. These studies are representative of the target
population. Case control, cross-sectional and cohort control studies are collectively referred to as observational studies.
Cross-sectional studies: Cross-sectional studies are the one which gives a snapshot of the study subjects in a single point of time. This type of study does not have a follow-up period.
Case-control studies: It is used to determine the degree of associations between various risk factors and outcomes. This type of 0studies can help to identify beneficial or harmful exposures; that is factors that affect the risk of disease. In the case-control study, there are two groups cases and controls. Cases are patients who have a particular disease/disability or condition. Controls are those patients who do not have the disease.
Cohort studies: These types of studies classify patients into two groups based on their exposure status. Cohorts are followed over time to see who develops the disease in the exposed and non exposed groups. It can be of two types, retrospective or prospective. Relative risk is the measure of effect for a cohort study.
Experimental studies: This study design is more powerful than other study designs. In this design, investigators
control over the allocation of exposure, its associated factors, and observation of the outcome.
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