In a cohort study, what is the definition of relative risk?

Relative risk is a measure used in cohort studies to compare the risk of a certain event or outcome occurring between two groups: those who have been exposed to a particular factor and those who have not. It quantifies the likelihood of the event happening in the exposed group relative to the unexposed group.

The correct definition of relative risk is that it is calculated by taking the incidence of the outcome in the exposed group and dividing it by the incidence in the unexposed group. This ratio provides insight into the strength of the association between the exposure and the outcome; a relative risk greater than 1 indicates a higher risk in the exposed group, while a relative risk less than 1 suggests a lower risk compared to the unexposed group.

This measure is particularly valuable in epidemiological research for understanding the impact of exposures on health outcomes and helps in identifying potential causal relationships.