<P> In fields such as epidemiology, social sciences, psychology and statistics, an observational study draws inferences from a sample to a population where the independent variable is not under the control of the researcher because of ethical concerns or logistical constraints . One common observational study is about the possible effect of a treatment on subjects, where the assignment of subjects into a treated group versus a control group is outside the control of the investigator . This is in contrast with experiments, such as randomized controlled trials, where each subject is randomly assigned to a treated group or a control group . </P> <P> The independent variable may be beyond the control of the investigator for a variety of reasons: </P>

What type of study is an observational study
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