Odds Ratio Calculator
Calculate the odds ratio to measure the association between exposure and outcome in case-control studies.
Calculate Odds Ratio
Table of Contents
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.
- Used in case-control studies
- Measures association strength
- Compares odds between groups
- Important in epidemiology
Interpreting Odds Ratio
OR > 1
Indicates increased odds of the outcome in the exposed group.
OR = 1
Indicates no difference in odds between groups.
OR < 1
Indicates decreased odds of the outcome in the exposed group.
Confidence Intervals
Help determine if the association is statistically significant.
Odds Ratio Formula
The odds ratio is calculated using the following formula:
Where:
- a = exposed with outcome
- b = exposed without outcome
- c = control with outcome
- d = control without outcome
Examples
Example 1 Increased Odds
Exposed Group: 40 with outcome, 60 without
Control Group: 20 with outcome, 80 without
OR = 2.67
The exposed group has 2.67 times higher odds of the outcome
Example 2 No Association
Exposed Group: 30 with outcome, 70 without
Control Group: 30 with outcome, 70 without
OR = 1.0
No difference in odds between groups
Example 3 Protective Effect
Exposed Group: 20 with outcome, 80 without
Control Group: 40 with outcome, 60 without
OR = 0.375
The exposed group has 0.375 times the odds of the outcome