Clinical Research Glossary

relative risk relative risk


The chance of a harmful event happening in one study group compared with another.

Example of relative risk in a sentence

If a relative risk is 1 the chance of an adverse event happening is the same across study groups.

More Info

For example, if a study finds that 20% of smokers develop lung cancer and 5% of non-smokers develop lung cancer, then we can calculate the relative risk of lung cancer in smokers versus non-smokers as:

Relative Risk = 20%/ 5% = 4

Thus, in this example, smokers are 4 times more likely to develop lung cancer than non-smokers.

Other info to think about when joining a study

You may see the term “relative risk” used in publications about the data and statistics of a research study. The results section of a publication will report the findings which will often include information about how many participants in one arm experienced a health event or problem versus participants in a comparison group. In general, however, “relative risk” 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 considering, 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.

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