In a case-control study of industrial solvent exposure and leukaemia, investigators match controls to cases on residence in the same housing colony, since colony location largely determines which residents worked at the solvent plant. This practice will most likely:

• A Increase statistical power by reducing confounding
• B Convert the design into a nested case-control study
• C Eliminate recall bias from exposure ascertainment
• D Bias the odds ratio toward the null and reduce the ability to detect a real association ✓

Explanation

Overmatching occurs when controls are matched on a variable closely tied to the exposure itself or lying on its causal pathway. Because cases and controls then become similar with respect to exposure probability, contrast between the groups is destroyed, driving the odds ratio toward unity and wasting statistical efficiency. Matching remains appropriate only for genuine confounders unrelated to the mechanism of exposure, and it has no effect on information bias whatsoever.

Reference: Gordis Epidemiology, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.