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How does relative risk measure the relationship between an exposure and a disease?

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In epidemiology, relative risk is a measure of association used to quantify the strength of the relationship between an exposure and a disease. It is specifically applied to categorical data derived from cohort studies.1

Relative risk is calculated by comparing the incidence of an event in an exposed group to the incidence in a baseline (unexposed) group:1

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

The resulting value indicates the strength and nature of the association:
* A value of 1: Indicates no association between the exposure and the disease.1
* A value greater than 1: Suggests that the exposed group is more likely to develop the disease than the unexposed group.1
* A value less than 1: Suggests that the exposure may have a protective effect, reducing the likelihood of the disease.1

While relative risk measures the strength of an association, it does not test for statistical significance; researchers often use a confidence interval for that purpose.1