How is relative risk calculated from the incidence of disease in exposed and unexposed groups?

In epidemiology, relative risk is a measure of association used to quantify the strength of the relationship between an exposure and a health outcome, such as a disease. It is calculated by dividing the incidence of the event in an exposed group by the incidence of the event in a baseline (unexposed) group.1

The formula is expressed as:

$$\text{Relative Risk}=\frac{\text{Incidence in exposed group}}{\text{Incidence in unexposed group}}$$

For example, if 10 out of 1,000 exposed individuals develop a disease and 2 out of 1,000 unexposed individuals develop the same disease, the relative risk is calculated as $(10/1000)/(2/1000)=5$. This indicates that those in the exposed group are five times more likely to develop the disease than those in the unexposed group. A relative risk of 1 suggests no association, while a value greater than 1 indicates an increased risk and a value less than 1 suggests a protective effect.1