Jak vypočítat Odds Ratio
Co je Odds Ratio?
The odds ratio (OR) measures the association between an exposure and an outcome in case-control studies. An OR > 1 indicates increased risk; OR < 1 indicates reduced risk; OR = 1 indicates no association.
Vzorec
OR = (a×d) / (b×c) from 2×2 contingency table
- a, b, c, d
- 2×2 table cells — [[a,b],[c,d]]
- OR
- odds ratio
Průvodce krok za krokem
- 1OR = (a×d) / (b×c)
- 2a=exposed cases, b=exposed controls, c=unexposed cases, d=unexposed controls
- 395% CI: e^(ln(OR) ± 1.96×SE)
- 4SE = √(1/a + 1/b + 1/c + 1/d)
Worked Examples
Vstup
a=100, b=50, c=200, d=300
Výsledek
OR = (100×300)/(50×200) = 3.0
Vstup
OR=1.5, CI=[1.1, 2.1]
Výsledek
50% increased odds; significant (CI excludes 1)
Frequently Asked Questions
What does an odds ratio of 1 mean?
OR=1 means no association between exposure and outcome. OR>1 suggests increased odds; OR<1 suggests decreased odds.
Is odds ratio the same as relative risk?
No, they're similar but different. Odds ratio compares odds; relative risk compares probabilities. OR ≈ RR when outcomes are rare.
How do I interpret an odds ratio of 2?
The odds of outcome in exposed group are 2 times the odds in unexposed group.
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