How is relative risk defined?

Relative risk is defined as the incidence of a particular outcome in the exposed group compared to the incidence of that same outcome in the non-exposed group. It is a measure used in epidemiology to determine the strength of the association between exposure and a certain outcome, such as a disease. Specifically, it quantifies how much more or less likely the outcome is to occur in the exposed group relative to the non-exposed group.

Calculating relative risk involves taking the incidence (or risk) in the exposed group and dividing it by the incidence (or risk) in the non-exposed group. A relative risk greater than 1 indicates an increased risk of the outcome due to the exposure, while a relative risk less than 1 indicates a decreased risk.

This definition underscores how we assess the impact of risk factors in clinical and public health research, allowing for a better understanding of causal relationships between variables. The other options do not correctly describe this ratio or the method for calculating it. For example, dividing the risk in the non-exposed by the risk in the exposed would provide an inverse measure that does not represent relative risk. Similarly, adding the risks or multiplying the incidences does not yield a relevant measure of risk comparison.