A study in which patients with colon cancer are asked what kinds of food they have eaten and the answers are compared with a selected control group.

• A. Systematic literature review
• B. Meta-analysis
• C. Cohort study
• D. Case control study

Answer: (D)

This scenario uses a case-control approach. It starts with people who have colon cancer and compares their past dietary exposures to those of a similar group without cancer. This design is built to study associations between a disease and prior exposures by looking backward in time, which is efficient for investigating rare diseases and allows you to assess multiple potential dietary factors from the same set of cases and controls. The usual measure of association derived from this design is the odds ratio.

A cohort study would instead follow a group of people over time from exposure onward to see who develops the disease, which is prospective and estimates risk rather than odds. A systematic literature review or meta-analysis compiles and analyzes results from many studies rather than collecting new exposure data from current cases and controls. Recall bias is a common concern here because dietary information is recalled after diagnosis, which can affect accuracy.