Community controls were preferred to hospital controls in a case–control study where the cases are derived from the hospital

OBJECTIVE: Cases and controls should be chosen from the same base population to reduce selection bias in case-control studies. For hospital cases, we examined how inferences drawn from a case-control study can differ by choice of hospital- vs. community-based controls. STUDY DESIGN AND SETTINGS: We used data from a case-control study that assessed risk factors for community-acquired pneumonia (CAP) hospitalization in Hamilton, Ontario, and …