1. What is Odds Ratio?

The Odds Ratio (OR) is a measure of association between an exposure and an outcome. It represents the odds that an outcome will occur given a particular exposure, compared to the odds of the outcome occurring in the absence of that exposure.

2. How Does the Calculator Work?

The calculator uses the Odds Ratio formula:

Where:

• \( a \) — Exposed with outcome (count)
• \( b \) — Exposed without outcome (count)
• \( c \) — Unexposed with outcome (count)
• \( d \) — Unexposed without outcome (count)

Explanation: The OR compares the odds of the outcome in the exposed group versus the unexposed group.

3. Interpretation of Odds Ratio

Details:

• OR = 1: No association between exposure and outcome
• OR > 1: Positive association (higher odds of outcome with exposure)
• OR < 1: Negative association (lower odds of outcome with exposure)

4. Using the Calculator

Tips: Enter counts for all four cells of the 2×2 table. All values must be non-negative integers. The calculator will return "NaN" if division by zero would occur.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between odds ratio and relative risk?
A: OR compares odds while RR compares probabilities. They approximate each other when outcomes are rare (<10%) but diverge for more common outcomes.

Q2: When should I use odds ratio?
A: OR is commonly used in case-control studies where relative risk cannot be calculated directly.

Q3: What does an OR of 2.5 mean?
A: The odds of the outcome are 2.5 times higher in the exposed group compared to the unexposed group.

Q4: How do I calculate confidence intervals for OR?
A: 95% CI = exp(ln(OR) ± 1.96 × √(1/a + 1/b + 1/c + 1/d))

Q5: Can OR be negative?
A: No, OR ranges from 0 to infinity, with 1 indicating no effect.