Relative Risk

Relative risk compares the probability of an outcome in a group that was exposed to a factor with the probability in a group that was not exposed. It works by taking two risks on the same scale and forming a ratio, so a value above 1 means the exposure is associated with a higher risk, a value below 1 means a lower risk, and a value of 1 means no difference. This is useful in studies that follow people over time, because it tells you how much more or less likely disease is in the exposed group.

Use relative risk in cohort studies, clinical trials, and other situations where you can directly measure incidence in exposed and unexposed groups. It is especially helpful when you want a simple comparison of disease risk between two groups.

• Using the number of cases instead of the incidence proportion in each group
• Dividing exposed risk by the total sample risk instead of the unexposed risk
• Interpreting relative risk as the same thing as absolute risk increase