Epidemiology & Public Health
Intermediate

Odds Ratio

Ratio of the odds of exposure among cases versus controls in a case-control study.

Formula

OR=a×db×cOR = \frac{a \times d}{b \times c}

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Variables

OROdds ratio
aExposed cases
bExposed controls
cUnexposed cases
dUnexposed controls

Example

a=40, b=20, c=10, d=30 → OR = (40×30)/(20×10) = 6

Did You Know?

For rare diseases (prevalence < 10 %), the odds ratio closely approximates the relative risk.

epidemiologyodds ratiocase-control

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