# Absolute risk

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Measure in clinical research

The group exposed to treatment (left) has 1/4 or 25% absolute risk of an adverse outcome (dark). The unexposed group (right) has 1/2 or 50% absolute risk of an adverse outcome.

**Absolute risk** (or AR) is the [probability](/source/Probability) or chance of an [event](/source/Event_(probability_theory)). It is usually used for the number of events (such as a disease) that occurred in a group, divided by the number of people in that group.[1]

Absolute risk is one of the most understandable ways of communicating health risks to the general public.[2]

In difference to absolute risk, the [relative risk](/source/Relative_risk) (RR) is the ratio of the probability of an [outcome](/source/Outcome_(probability)) in an exposed group to the probability of the outcome in an unexposed group.

## See also

- [Absolute risk reduction](/source/Absolute_risk_reduction)

- [Relative risk reduction](/source/Relative_risk_reduction)

## References

1. **[^](#cite_ref-IEA_Dictionary_of_Epidemiology_1-0)** Porta, Miquel, ed. (2014). [*A dictionary of epidemiology*](http://irea.ir/files/site1/pages/dictionary.pdf) (PDF) (Six ed.). Oxford: Oxford University Press. [ISBN](/source/ISBN_(identifier)) [9780199976720](https://en.wikipedia.org/wiki/Special:BookSources/9780199976720). Retrieved 11 November 2017.

1. **[^](#cite_ref-Trevena_2006_2-0)** Trevena, LJ; Davey, HM; Barratt, A; [Butow, P](/source/Phyllis_Butow); Caldwell, P (February 2006). ["A systematic review on communicating with patients about evidence"](https://doi.org/10.1111%2Fj.1365-2753.2005.00596.x). *Journal of Evaluation in Clinical Practice*. **12** (1): 13–23. [doi](/source/Doi_(identifier)):[10.1111/j.1365-2753.2005.00596.x](https://doi.org/10.1111%2Fj.1365-2753.2005.00596.x). [PMID](/source/PMID_(identifier)) [16422776](https://pubmed.ncbi.nlm.nih.gov/16422776).

## Further reading

- Woloshin, Steven; Schwartz, Lisa M.; [Welch, H. Gilbert](/source/H._Gilbert_Welch) (2008). [*Know Your Chances: Understanding Health Statistics*](https://pubmed.ncbi.nlm.nih.gov/23469386/). Berkeley (CA): University of California Press. [PMID](/source/PMID_(identifier)) [23469386](https://pubmed.ncbi.nlm.nih.gov/23469386).

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