Relative risk ( RR )

Relative risk is the ratio between the rate of disease in the population exposed to a particular factor and the rate in those not exposed.

• Given the following:
  • a = suspected cause present and disease present
  • b = suspected cause present and disease absent
  • c = suspected cause absent and disease present
  • d = suspected cause absent and disease absent
  • total disease present = a+c
  • total disease absent = b+d
  • total suspected cause present = a+b
  • total suspected cause absent = c+d
    
    
• relative risk (RR) = a / (a+b) divided by the result of c/ (c+d)

If:

the RR =1, or the confidence interval (CI) includes 1, then there is no significant difference between the treatment and control groups

the RR>1 and the CI does not include 1, events are significantly more likely in the treatment group than the control group

the RR<1 and CI does not include 1, events are significantly less likely in the treatment group than the control group