An observational study is one that draws inferences from a small sample of a population where the independent variable is not under the control of the researcher due to logistical constraints or ethical concerns. A common observational study that is conducted is about the possible result of a particular set of experiments where the assignment of subjects in a group containing whirlpool is selected subjects versus a control group is outside the control of the investigator. An observation study is in stark contrast with experiments like the randomized controlled trials where each individual subject is assigned at random to a treated group or a control group. Since observation studies do not have an assignment mechanism inferential analysis poses some difficulties.
There are seven types of observational studies:
- Case-control study – This is a study that was originally developed in epidemiology, in which 2 existing groups that have different outcomes are identified and compared based on some supposed causal attribute.
- Cross-sectional study – This involves the collection of data from a population, or a representative subset, at a particular point in time.
- Longitudinal study – This is a correlational research study involving repeated observations of the same variables over a long period of time. Cohort and Panel studies are 2 particular forms of a longitudinal study.
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