# Attributable Risk

In epidemiology, attributable risk is the difference in rate of a condition between an exposed population and an unexposed population. Attributable risk is mostly calculated in cohort studies, where individuals are assembled on exposure status and followed over a period of time. Investigators count the occurrence of the diseases. The cohort is then subdivided by the level of exposure and diseases frequency is compared subgroups. One is considered exposed and another unexposed. The formula commonly used in Epidemiology books for Attributable risk is Ie - Iu = AR, where Ie = Incidence in exposed and Iu = incidence in unexposed. We can calculate AR percent once we calculate AR. The formula for that is 100*(Ie - Iu)/Ie .

Note: Ie is calculated by simply dividing the number of exposed people who get the disease by the total number who are exposed (N-exposeddis / N-exposedtot = Ie). Similarly, the Iu is calculated by dividing the number of unexposed people who get the disease by the total number who are not exposed (N-unexposeddis / N-unexposedtot = Iu).

The concept was first proposed by Levin in 1953.

Read more about Attributable RiskDiversity of Interpretation, Uses, Combined PAR, Worked Example

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... In a cohort study, individuals with exposure to a risk factor (Exposure +) are followed for a certain number of years to see if they develop a certain disease or outcome (Disease +) ... control group of individuals who are not exposed to the risk factor (Exposure −) are also followed ... The incidence with exposure is The incidence without exposure To determine the relative risk, divide the incidence with exposure by the incidence without exposure relative risk To determine attributable risk ...

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