What does a relative risk equal to one signify?

A relative risk equal to one indicates that there is no difference in the risk of the disease between the exposed group and the unexposed group. This means that the exposure being studied does not appear to influence the likelihood of developing the disease. In epidemiological studies, a relative risk less than one suggests a protective effect, while a relative risk greater than one indicates an increased risk. Therefore, a relative risk of one serves as a benchmark for establishing that there is no evidence of an association between the exposure and the disease outcome. This concept is fundamental in helping researchers understand the impact of various risk factors on health outcomes.