Context: Let's say we have a neurologist from Hospital X who wants to investigate the relationship between cancer and stroke risk in the general population with a case-control study. The cases are all the neurologist's patients with a history of strokes. The control group consists of all her patients without a stroke history. Both groups were assessed for cancer.

How it Relates to Selection Bias: Patients in the hospital may be more predisposed to those conditions or may have been brought to the hospital for those conditions. Therefore, they may be overrepresented in the study compared to the general population.