What type of observational study identifies subjects with a disease and looks back to find exposure to risk factors?

The correct choice is the case-control study, which is specifically designed to identify subjects who have a particular disease (the cases) and then look backwards to determine their previous exposure to potential risk factors. In this type of study, researchers compare the cases with a control group of subjects who do not have the disease. By examining the past exposure history of both groups, researchers can identify potential associations between risk factors and the disease.

This method is particularly useful for studying diseases that are rare or have a long latency period, as it allows researchers to efficiently gather data on risk factors that may have contributed to the development of the disease. Case-control studies are often used in epidemiology to generate hypotheses for further research.

In contrast, cross-sectional studies assess data at a single point in time and do not provide a temporal relationship between exposure and outcomes. Longitudinal studies track subjects over time to observe outcomes as they occur and are generally more resource-intensive. Cohort studies follow a group of subjects who are initially free of the disease and monitor them for the development of outcomes based on their exposure status. While both longitudinal and cohort studies can provide valuable insights, they do not analyze pre-existing cases in the same retrospective manner as case-control studies.