Relative risk (RR)

Relative Risk (RR) is a measure used in epidemiology to determine the strength of association between exposure and disease. It is commonly used in cohort studies.

RR = (Incidence of disease in unexposed group) / (Incidence of disease in exposed group) 

RR = [a/(a+b)] / [c/(c+d)] 

where:

• a = Exposed individuals who develop the disease

• b = Exposed individuals who do not develop the disease

• c = Unexposed individuals who develop the disease

• d = Unexposed individuals who do not develop the disease

Interpretation of relative risk (RR): 

• RR = 1 → No association (risk is the same in both groups)

• RR > 1 → Exposure increases the risk of disease (positive association)

• RR < 1 → Exposure is protective against disease (negative association)