Biostats Calculator

Features > Odds ratio

An odds ratio measures the difference in proportions of one group (cases) that has a particular characteristic compared to a reference group (controls). It is typically used in case-control studies to measure the effect of exposure to risk factor. Here, the cases represent people with a certain outcome while the controls represent all people. A statistically significant odds ratio indicates that the risk factor is associated with the outcome.

After selecting Odds ratio from the menu, simply enter the number of exposed and unexposed individuals in the case and control groups. Biostats Calculator will calculate the difference between the proportions and perform a hypothesis test to determine whether it is statistically significant.

Biostats Calculator reports:

• The odds ratio (the odds of exposure for cases divided by the odds of exposure for controls)
• Confidence intervals for the odds ratio, at the 90%, 95% and 99% confidence levels
• The p value, indicating how likely it is that the observed difference would occur due to chance alone
• whether the result is significant at the 95% confidence level

Biostats Calculator can perform this test and 11 others from the convenience of your iPhone or iPod Touch. Buy it today!

Related tests

• Relative risk - a preferred outcome measure for randomized trials and cohort studies
• Chi-square test and Fisher's exact test - detect a difference in proportions between any number of groups