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# 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

Last reviewed 08/2020