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Odds Ratio Formula:
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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.
The calculator uses the odds ratio formula:
Where:
P-value calculation: The calculator provides an approximate p-value based on chi-square test to assess statistical significance.
OR = 1: No association between exposure and outcome
OR > 1: Exposure associated with higher odds of outcome
OR < 1: Exposure associated with lower odds of outcome
P-value < 0.05: Typically considered statistically significant
Tips: Enter counts for all four cells of the 2×2 table. All values must be non-negative integers. The calculator will compute both the odds ratio and an approximate p-value.
Q1: What's the difference between odds ratio and relative risk?
A: Odds ratio compares odds, while relative risk compares probabilities. They are similar when outcomes are rare but diverge as outcomes become more common.
Q2: When should I use Fisher's exact test instead of chi-square?
A: Use Fisher's exact test when sample sizes are small (expected counts <5 in any cell).
Q3: How should I interpret a non-significant p-value?
A: A non-significant result (p ≥ 0.05) suggests the observed association could be due to chance, but doesn't prove no association exists.
Q4: What are confidence intervals for odds ratios?
A: Confidence intervals provide a range of plausible values for the true odds ratio. A 95% CI that doesn't include 1 indicates statistical significance.
Q5: Can I use this for case-control studies?
A: Yes, odds ratios are particularly useful for case-control studies where relative risk cannot be directly calculated.