Which of the following measures cannot be directly calculated from a conventional case-control study?

• A Odds ratio
• B Attributable fraction among the exposed
• C Population attributable risk percent using Levin's formula
• D Incidence rate of disease in the exposed group ✓

Explanation

A case-control study begins with diseased and non-diseased individuals and works backward to exposure status, so it provides no denominator of person-time or population at risk from which incidence can be computed. Incidence rates require a cohort or cross-sectional enumeration of the source population. The odds ratio is the native measure of case-control data, and the attributable fraction among the exposed can be derived from the odds ratio when disease is rare, just as Levin's formula derives population attributable risk percent from exposure prevalence and the odds ratio.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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