Retrospective studies are observational studies that look back in time. In retrospective studies, researchers start with a population that’s already experienced a given outcome, such as cancer, and try to go back in time to find exposures that have contributed. In many cases, data used in retrospective studies was generated before the study was conceived, so it isn’t always a perfect fit. And researchers may not have all the information they need to definitively answer a question. In other cases, like outbreak investigations, researchers rely on retrospective data gathering to help them determine the source of an illness. They start with sick people and work back in time to find the source of the illness.
