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 following formulas:

Where:

• \( a \) — Exposed with outcome
• \( b \) — Exposed without outcome
• \( c \) — Unexposed with outcome
• \( d \) — Unexposed without outcome
• \( z \) — Z-score for desired confidence level (1.96 for 95% CI)

3. Importance of Confidence Interval

Details: The confidence interval provides a range of plausible values for the odds ratio. If the interval includes 1, the association is not statistically significant at the chosen confidence level.

4. Using the Calculator

Tips: Enter the counts in each category (a, b, c, d) and the desired Z-score (1.96 for 95% CI, 1.645 for 90% CI, 2.576 for 99% CI). All counts must be non-negative integers.

5. Frequently Asked Questions (FAQ)

Q1: What does an OR of 1 mean?
A: An OR of 1 means there is no association between the exposure and outcome.

Q2: What's the difference between OR and relative risk?
A: OR compares odds, while relative risk compares probabilities. They are similar when outcomes are rare but diverge for common outcomes.

Q3: How do I interpret the confidence interval?
A: If the 95% CI doesn't include 1, the OR is statistically significant at p<0.05.

Q4: When should I use this calculator?
A: For case-control studies or when you have counts in a 2×2 contingency table.

Q5: What are common Z-score values?
A: 1.645 (90% CI), 1.96 (95% CI), 2.576 (99% CI).