How is relative risk (RR) calculated?

Relative risk (RR) is a measure used in epidemiological studies that compares the probability of an event occurring in two groups, typically a treatment group and a control group. It is calculated by taking the ratio of the risk (incidence) of an event in the exposed group to the risk of the same event in the unexposed group.

To break down the calculation: The first part of the fraction, a/(a + b), represents the incidence rate of the event in the exposed group (where 'a' is the number of events in the exposed group, and 'b' is the number of non-events in the exposed group). The second part of the fraction, c/(c + d), reflects the incidence rate of the event in the unexposed group (where 'c' is the number of events in the unexposed group, and 'd' is the number of non-events in the unexposed group). By dividing these two rates, researchers can determine how much more or less likely the event is to occur in the exposed group relative to the unexposed group.

This calculation is crucial in clinical studies as it helps to understand the effectiveness of treatments or the impact of risk factors on health outcomes. A