Q: What is a retrospective study? How is it different from a prospective study?
A retrospective study design involves collecting data from the past to examine exposures to suspected risk or protection factors in relation to an outcome that is established at the beginning of the study. In this kind of study, the outcome has already happened when the study is being conducted. Individuals are sampled and information about them is collected from the past. This data is then analyzed to understand what could have led to the outcome. In medicine and psychology, medical records and interviews could be used to collect past information about a group of patients with a particular medical condition. The study goes back to the time when they were disease-free, and data from this time leading up to the outcome are collected and analyzed to understand the onset and progress of the disease/condition.
In prospective studies, on the other hand, the outcome has not yet happened at the time of study. Individuals are followed over a long period of time and are observed for the development of the outcome. Data is collected as their symptoms, characteristics, or circumstances change and are related to suspected risk or protection factors to understand the possible causes of the onset and development of the outcome.
Prospective studies can be interventional, observational, or a mix of the two; however, retrospective studies are always observational.
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