#### II. Definition

1. Relative Risk
1. Ratio of probability of an event in an exposed group to that in an unexposed group

#### III. Evaluation

1. Calculation
1. Relative Risk = P(disease I exposure) / P(disease I No exposure)
2. Example
1. Exposure to Substance X
1. Disease Y Contracted in 25
2. Disease Y NOT Contracted in 75
2. NO Exposure to Substance X
1. Disease Y Contracted in 10
2. Disease Y NOT Contracted in 190
3. Probabilities
1. P(disease | exposure) = 25 / (25 + 75) = 0.25
2. P(disease | No exposure) = 10 / (10 + 190) = 0.05
4. Conclusion
1. Relative Risk = P(disease I exposure) / P(disease I No exposure) = 0.25/0.05 = 5
2. Patients exposed to Substance X are 5 times more likely to develop disease Y

#### V. References

1. Desai (2014) Clinical Decision Making, AMIA’s CIBRC Online Course

### Ontology: Relative Risk (C0242492)

 Definition (NCI_NCI-GLOSS) A measure of the risk of a certain event happening in one group compared to the risk of the same event happening in another group. In cancer research, risk ratios are used in prospective (forward looking) studies, such as cohort studies and clinical trials. A risk ratio of one means there is no difference between two groups in terms of their risk of cancer, based on whether or not they were exposed to a certain substance or factor, or how they responded to two treatments being compared. A risk ratio of greater than one or of less than one usually means that being exposed to a certain substance or factor either increases (risk ratio greater than one) or decreases (risk ratio less than one) the risk of cancer, or that the treatments being compared do not have the same effects. Concepts Quantitative Concept (T081) MSH D012306 English Relative Risks, Risk, Relative, Risks, Relative, RELAT RISK, relative risk, Relative Risk, risk ratio French Risque relatif German Relatives Risiko Italian RR, Rischio relativo Norwegian Relativ risiko Dutch Risico, relatieve