Which of the following best defines a case control study?

A case-control study is best defined as a study that compares individuals with a specific condition (the cases) to those without the condition (the controls). This design is particularly useful in identifying potential risk factors or causes for a condition, as it allows researchers to look back in time to examine differences between the two groups concerning their exposure to various factors.

In a case-control study, the researcher starts with knowledge of the outcome (whether the individuals have the condition or not) and then investigates prior exposure to potential risk factors, thus offering insight into the relationships between variables. This design is often used in epidemiology to study rare diseases or outcomes, as it is typically more feasible to look back in this way rather than to conduct a longitudinal study that follows participants over time from exposure to the development of the outcome.

The other options represent different research designs. A study comparing multiple treatments focuses on treatment efficacy rather than the presence of a condition. A long-term survey is not focused on the relationship between cases and controls but rather on data collection over time. A qualitative study based on interviews emphasizes understanding perspectives or experiences rather than establishing causal relationships based on case-control comparisons.