U01.06.009 Attributable risk

Attributable risk (AR) is a measure used in epidemiology to quantify the difference in the risk of a particular outcome between an exposed group and an unexposed group. It indicates the proportion of the incidence of a condition (like a disease) that can be attributed to a specific exposure.

Calculation of Attributable Risk

Attributable risk is calculated by subtracting the risk in the unexposed group from the risk in the exposed group.

Formula:

Attributable Risk (AR) = Risk in Exposed Group - Risk in Unexposed Group

For example, if the risk of lung cancer in smokers is 21% and the risk in nonsmokers is 1%, the attributable risk is:

AR = 21% - 1% = 20%

This means that 20% of the risk of lung cancer in smokers can be attributed to smoking.

Example Table: Attributable Risk Calculation

Group	Risk of Lung Cancer	Attributable Risk Calculation
Smokers	21%	`21% - 1% = 20%`
Nonsmokers	1%

Example Table: Attributable Risk Calculation

Points to Remember

Attributable Risk (AR) quantifies the proportion of disease risk that can be attributed to a specific exposure.
It is an important measure for assessing the public health impact of eliminating a risk factor.
AR is different from Relative Risk (RR), which compares the risk in exposed versus unexposed groups but does not measure the absolute difference.

Bibliography

Rothman, K. J., Greenland, S., & Lash, T. L. (2008). Modern Epidemiology (3rd ed.). Philadelphia: Lippincott Williams & Wilkins.
Gordis, L. (2014). Epidemiology (5th ed.). Philadelphia: Elsevier/Saunders.

USMLE Step 1 Review Series

Curriculum

U01.06.009 Attributable risk

Calculation of Attributable Risk

Example Table: Attributable Risk Calculation

Points to Remember

Bibliography

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