What is a case-control study?

A case-control study is a research design that compares individuals who have a specific condition or disease (the cases) to those who do not have the condition (the controls). This type of study is particularly useful for identifying factors that may contribute to the development of a disease. By examining the differences in exposure to potential risk factors between the two groups, researchers can gain insights into causal relationships and associations.

In case-control studies, the participants are selected based on the outcome of interest, and their past exposures or characteristics are investigated to determine what might have led to the condition. This design is often employed in epidemiological research, especially when investigating rare diseases, as it allows researchers to efficiently gather data without requiring a long follow-up period as would be necessary in cohort studies.

The other choices present different types of research methodologies. Longitudinal studies track subjects over time to observe changes or developments, while survey methods focus on collecting data through questionnaires rather than direct comparisons of cases and controls. Studies focusing solely on the effects of treatments usually pertain to clinical trials rather than case-control studies. Therefore, the distinction and focus provided in choice A accurately reflects the core characteristics of a case-control study.