How does the Odds Ratio Calculator work?

OR = (a×d) / (b×c) Then: a=exposed cases, b=exposed controls, c=unexposed cases, d=unexposed controls Then: 95% CI: e^(ln(OR) ± 1.96×SE) Then: SE = √(1/a + 1/b + 1/c + 1/d).

Can you give an example of how to use the Odds Ratio Calculator?

Example: Input a=100, b=50, c=200, d=300 gives a result of OR = (100×300)/(50×200) = 3.0.

Is the Odds Ratio Calculator free to use?

Yes — completely free with no registration, download, or subscription required. All calculations happen instantly in your browser.

How accurate is the Odds Ratio Calculator?

Our Odds Ratio Calculator uses verified mathematical formulas and is accurate to multiple decimal places. Results are calculated in real-time using the same methods used by professionals.

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Odds Ratio Calculator

2×2 contingency table: a=exposed/case, b=exposed/control, c=unexposed/case, d=unexposed/control

a (exposed, case)

b (exposed, control)

c (unexposed, case)

d (unexposed, control)

✓Odds Ratio

Odds Ratio

3.0000

ln(OR)

1.0986

95% CI

[2.044, 4.403]

OR = 1: no association | OR >1: positive association | OR <1: negative association

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.

Symbol	Name	Unit	Description
a, b, c, d	2×2 table cells	—	[[a,b],[c,d]]
OR	odds ratio	—	—

OR value	Association	Meaning
< 1	Negative	Exposure protective
= 1	None	No association
1.1–1.5	Weak positive	Slight increased risk
1.5–3.0	Moderate	Meaningful association
> 3.0	Strong	Strong association

References

›Odds ratio — Wikipedia

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Odds Ratio Calculator