Final answer:
A retrospective study is conducted after a disease outbreak to investigate the characteristics and potential causes of illness in the affected population. It is comparatively quicker and less costly than other epidemiological study types but may have limitations due to recall or selection biases.
Step-by-step explanation:
In epidemiology, a retrospective study occurs after a disease outbreak to determine the characteristics of ill people such as age, sex, personal habits, location, etc. A retrospective study, also known as a case-control study, looks back in time to examine exposures to suspected risk factors or protections about an outcome that is established at the start of the study. Many retrospective studies aim to identify causative factors or trigger events for diseases. Researchers compare the medical histories of people who have the disease (the cases) with those of people who do not (the controls). This method contrasts with prospective studies, like cohort studies, where subjects are followed over time. Case-control studies are particularly useful for understanding outbreaks because they can be conducted relatively quickly and are not as costly as long-term cohort studies. These studies provide quick and often powerful results but may be limited by bias in the recall or selection of cases and controls.