Relative risk is a measure used in epidemiology to compare the risk of a certain event occurring in two different groups. It is calculated by dividing the risk of the event in the exposed group by the risk in the unexposed group. For example, if a study examines the risk of developing heart disease in smokers versus non-smokers, relative risk helps quantify how much more likely smokers are to develop the condition. A relative risk greater than 1 indicates a higher risk in the exposed group, while a value less than 1 suggests a lower risk. A relative risk of 1 means there is no difference in risk between the two groups. Understanding relative risk is essential for making informed decisions about health behaviors and interventions.