For example, retrospective studies into military veterans with cancer were able to provide information into how exposure to the toxic herbicide Agent Orange was causally linked to increased incidence of cancer amongst exposed U.S. Many important studies into occupational hazards have been retrospective studies. This makes them useful for conducting research into conditions that would be too resource-intensive to study using prospective methods. One benefit is that they allow researchers to select the desired number of people with the condition they are studying, which means that the overall number of people in the study can be significantly less than in a prospective study, and are quicker to complete.

Retrospective studies have both benefits and drawbacks. For example, a retrospective study of breast cancer patients would involve comparing a group of people with breast cancer to a similar group of people without breast cancer, while a prospective study would involve recruiting a single group of people without breast cancer and monitoring them for an extended period in order to try and discover insights into why some of them developed breast cancer during the study. Retrospective studies are so-named because they involve looking backwards at the histories of the people being studied, rather than monitoring a group of people over an extended period (a prospective study).

Retrospective study example