Which observational study type is most appropriate when a researcher wants to study a rare disease and compare prior exposures between those with and without the disease?

• A. Ecological time-series analysis at the national level, because individual-level exposure data are not required for rare disease studies
• B. Case-control study, because it identifies cases with the disease and suitable controls to retrospectively compare prior exposures
• C. Prospective cohort study of the general population, because rare diseases are best studied by following everyone forward without selecting cases
• D. Case study of a single patient to generalize risk factors for the entire population

Answer: (B)