Clinical Research Glossary

odds ratio odds ratio


The chance of a health event happening in one group compared with the chance of the same event happening in another group.

Example of odds ratio in a sentence

An odds ratio is a measure of the link between an exposure and an event.

More Info

An odds ratio compares the odds of two different groups. It is used to describe the association of exposure to one variable of interest (e.g. health characteristic, aspect of medical history) to a disease or disorder, compared with the lack of the variable with the disease or disorder. It also looks at the strength of that association.

The odds ratio can also be used to determine whether a specific exposure is a risk factor for a particular outcome. For instance, the ratio of the odds of lung cancer in smokers divided by the odds of lung cancer in non-smokers is 14.

Two events are not related if the odds ratio equals 1, i.e., the odds of an event are the same in either the presence or absence of the other event.

If the odds ratio is greater than 1, then two events are positively associated (correlated), i.e., The presence of one event increases the chance of the other one being present.

Other info to think about when joining a study

You may see the term “odds ratio” when reading results information of a research study. The results section of a publication will talk about the data and statistics. “Odds Ratio” is a technical math term and will not usually be used in materials designed especially for patients and participants.

If you see this word in a study document for a study you are thinking about joining, enrolled in, or completed, you can ask the researcher or study team any questions you might have.

An icon consisting of a circle with a calculator, graph paper with a bar chart and a bell curve drawn on, and a pencil. This icon represents all the math terms in this glossary.
This graphic represents math and statistics terms in this glossary.

Was this entry helpful?

Thanks for your feedback!