What is the formula for calculating attributable risk?

Attributable risk is a measure that quantifies the excess risk of a particular outcome (such as a disease) in a population exposed to a risk factor compared to a population not exposed. It is essential in epidemiology for understanding the impact of a risk factor on health outcomes.

The formula for calculating attributable risk involves determining the difference between the incidence rate of the outcome in the exposed group (those with the risk factor) and in the unexposed group (those without the risk factor).

The terms in the formula represent the following:

• 'a' is the number of individuals with the outcome who were exposed to the risk factor.

• 'b' is the number of individuals without the outcome who were exposed.

• 'c' is the number of individuals with the outcome who were not exposed.

• 'd' is the number of individuals without the outcome who were not exposed.

Using these terms:

• The proportion of individuals with the outcome among the exposed group is calculated as a/(a+b).

• The proportion of individuals with the outcome among the unexposed group is calculated as c/(c+d).

Thus, the attributable risk can be calculated as follows:

[ \text{Attributable Risk} = \left(\frac