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. An OR of 1 means no difference between groups.

3. Interpretation of Odds Ratio

Details:

• OR > 1: Higher odds of outcome with exposure
• OR = 1: No difference in odds between groups
• OR < 1: Lower odds of outcome with exposure

The further from 1, the stronger the association.

4. Using the Calculator

Tips: Enter counts for all four cells (a, b, c, d) as whole numbers. All values must be ≥0, and at least one of b or c must be >0.

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 risk when outcomes are common (>10%).

Q2: When should I use odds ratio?
A: OR is commonly used in case-control studies and logistic regression analysis.

Q3: How do I interpret an OR of 2.5?
A: The exposed group has 2.5 times the odds of the outcome compared to the unexposed group.

Q4: What are confidence intervals for OR?
A: Typically reported as 95% CI. If it includes 1, the result may not be statistically significant.

Q5: Can OR be negative?
A: No, OR ranges from 0 to infinity (with 1 as the null value).