Definition of risk ratio A risk ratio (RR), also called relative risk, compares the risk of a health event (disease, injury, risk factor, or...
death) among one group with the risk among another group. It does so by dividing the risk (incidence proportion, attack rate) in group 1 by the risk (incidence proportion, attack rate) in group 2 . The two groups are typically differentiated by such demographic factors as sex (e.g., males versus females) or by exposure to a suspected risk factor (e.g., did or did not eat potato salad). Often, the group of primary interest is labeled the exposed group, and the comparison group is labeled the unexposed group. Method for Calculating risk ratio The formula for risk ratio (RR) is:
Risk of disease (incidence proportion, attack rate) in group of primary interest / Risk of disease (incidence proportion, attack rate) in comparison group
A risk ratio of 1.0 indicates identical risk among the two groups. A risk ratio greater than 1.0 indicates an increased risk for the group in the numerator, usually the exposed group. A risk ratio less than 1.0 indicates a decreased risk for the exposed group, indicating that perhaps exposure actually protects against disease occurrence.
As book " Principles of Epidemiology in Public Health Practice "