Relative Risk

Relative Risk

Incidence of the disease in the exposed / Incidence of the disease in the unexposed.

Odds Ratio

Rates Ratio

RR Value

IR = IRe/IRo

Risk Ratio

  • CI and IR

Rate Ratio

CI = CIe/CIo = (a/(a+b)) / (c/(c+d))

IR = IRe/IRo

RR = 1: The disease and risk factor are unrelated

RR < 1: There’s a ‘negative association’ between the risk factor and the disease

RR > 1: There’s a strong association between disease and risk factor

IRe = Incidence Rate in Exposed

This can be used if we have IR instead of CI

IRo = Incidence Rate in Unexposed

"Those exposed to [exposure] have [RR] times the risk of developing [outcome], compared to the unexposed"

OR Value

OR = 1: No Difference

OR < 1: DECREASED Odds in Exposed

OR > 1: INCREASED Odds in Exposed

  • No Incidence = No Risk
  • Case-Control or Cross-Sectional
  • We must estimate risk using odds

We need INCIDENCE (CI or IR)

Cohort or **

OR = (a/c) / (b/d) = ad/bc

"Those exposed to [exposure] had [OR] times the odds of developing [outcome], compared to the unexposed"