Which description best defines a case-control study?

• A. Study of past mortality or morbidity trends to permit estimates of the occurrence of disease in the future
• B. Analysis of previous research in different places and under different circumstances to permit the establishment of hypotheses based on cumulative knowledge of all known factors
• C. Obtaining histories and other information from a group of known cases and from a comparison group to determine the relative frequency of a characteristic or exposure under study
• D. Study of the incidence of cancer in men who have quit smoking

Answer: (C)

Case-control studies compare exposure histories between people with the disease (cases) and those without it (controls) to see how common a factor is in each group. By looking backward from outcome to exposure, you can estimate the strength of the association between a factor and the disease, typically using an odds ratio. This design is especially efficient for studying rare diseases or when time and resources are limited, because you start with the outcome and don’t have to follow people into the future. It also lets you examine multiple exposures for a single outcome. However, it relies on accurate recall and careful selection of controls to avoid bias.

The description provided matches this approach: obtaining histories from known cases and a comparison group to determine the relative frequency of an exposure under study. The other options refer to different study designs—trends and forecasting, literature reviews, or prospective cohorts looking at incidence—which are not case-control studies.