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 standard odds ratio formula:

Where:

• \( a \) — Number of exposed individuals with outcome
• \( b \) — Number of exposed individuals without outcome
• \( c \) — Number of unexposed individuals with outcome
• \( d \) — Number of unexposed individuals without outcome

Explanation: The odds ratio 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 (exposure may increase outcome risk)
• OR < 1: Negative association (exposure may decrease outcome risk)

4. Using the Calculator

Tips: Enter counts for each cell in the 2×2 contingency table. All values must be non-negative integers. The calculator will return "N/A" if division by zero would occur.

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 approximates RR when outcome is rare (<10%).

Q2: When should I use odds ratio?
A: OR is commonly used in case-control studies where relative risk can't 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: Can OR be less than 1?
A: Yes, an OR < 1 suggests the exposure might be protective against the outcome.

Q5: How precise is the odds ratio?
A: Precision depends on sample size. Confidence intervals should be calculated to assess precision.