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:

• \( a \) — Number of events in group 1
• \( b \) — Number of non-events in group 1
• \( c \) — Number of events in group 2
• \( d \) — Number of non-events in group 2

Explanation: The odds ratio compares the odds of an event occurring in one group versus another group.

3. Interpretation of Odds Ratio

Details:

• OR = 1: No association between exposure and outcome
• OR > 1: Higher odds of outcome with exposure
• OR < 1: Lower odds of outcome with exposure

4. Using the Calculator

Tips: Enter counts for all four cells in the 2×2 contingency table. All values must be non-negative integers.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between odds ratio and relative risk?
A: Odds ratio compares odds, while relative risk compares probabilities. OR overestimates RR when outcomes are common (>10%).

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 = e^{[ln(OR) ± 1.96 × SE(ln(OR))]}, where SE(ln(OR)) = √(1/a + 1/b + 1/c + 1/d)

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