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Why should controls in a case-control study come from the same source population as cases?

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Know the investigations of researchers using genomic information to reconstruct the cause and transmission routes of the bubonic plague and the Black Death — epidemiology Researchers using genomic information to trace the transmission routes in past epidemics of plague.

In a case-control study, selecting controls from the same source population as the cases is essential to ensure the validity of the study results.

The primary goal of this selection process is to prevent selection bias. If controls are not representative of the population that gave rise to the cases, the study may suffer from confounding, where observed correlations between an exposure and a disease are actually caused by unrelated factors rather than the exposure itself. By drawing both groups from the same source, researchers ensure that the controls are comparable to the cases, which allows for a more accurate calculation of the odds ratio.1

When cases and controls are not properly matched or drawn from the same population, the resulting distortion can lead to incorrect conclusions about the relationship between a suspected risk factor and the disease of interest.1