What is an observational study?


           Observational studies are the primary type of epidemiological study used to research determinants of outcome. There are several types of observational studies, which Dr. Robert Friis and the Aschengrau and Seage text describe.

            Like all epidemiological studies, an observational study studies causes, preventions, and treatments for outcome. What makes the study observational (and not experimental) is that the investigator passively observes as nature takes its course (Aschengrau & Seage, 2007, p. 137).

            Observational studies can be prospective or retrospective. In some cases, studies are ambi-directional and thus have elements of both prospective and retrospective studies (such as when exposure has happened but subjects are followed to observe the outcomes of the exposure).

            A prospective study is a study design that studies subjects going forward in time. That is, researchers group subjects based on their exposure (to either risk or protective factors) and follow the impact of the exposure over time (Cwikel, 2006).In other words, investigators recruit subjects and gather study data going forward (as opposed to looking back at past events).

            In a retrospective study, investigators study subjects and occurrences that have already happened (by looking back at data, records, or self-reports) and the exposure and outcome have both occurred.