The main aim of these studies is not only to describe and express the status of the present situation, but also to identify and compare the relationships between two or more variables and their impact in different groups.
The important point is that in these studies, the researchers observe the cases and collects the necessary data to come to the conclusion about the investigated phenomenon. This means that the researcher does not manipulate the research condition and it is out of his control to assign the participants into treated and control groups.
These studies seek to discover the relationship between the outcome and the exposure of the investigated phenomenon. In medical science studies, the phenomenon is called “disease” and effective factors are named “risk factors”.
Direction and timing are two important factors in the categorization of analytic observational studies. Considering direction, there are three categories, namely forward, backward, and non-directional ones. Regarding timing, there are also three types of research as follows:
Historical studies: Both the exposure and the outcome occur before the study.
Concurrent studies: Both the exposure and the outcome occur at the given time of the study.
Mixed time study: Exposure has sometimes occurred in the past, but the outcome is synchronous with the study, or a number cases are with simultaneous exposure and outcome while others are with historical exposure and outcome.
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