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An observational study can be used to describe many designs that are not randomized trials (eg, cohort studies or case-control studies that have a...
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An observational study can be used to describe many designs that are not randomized trials (eg, cohort studies or case-control studies that have a goal of establishing causation, studies of prognosis, studies of diagnostic tests, and qualitative studies). The term is most often used in the context of cohort studies and case-control studies in which patient or caregiver preference, or happenstance, determines whether a person is exposed to an intervention or putative harmful agent or behavior (in contrast to the exposure’s being under the control of the investigator, as in a randomized trial).