Odds Ratio (OR)
The Odds Ratio gives the radio with which "cases" are exposed relatively to controls.
- With an OR of 1 the part of exposed persons in both groups has been equal.
- With OR less than 1 the part of exposed persons under the cases was less, with OR higher than 1 more than under the controls.
By means of a significance test one can check how statistically important this difference is. For rare diseases the OR can be set equal to the RR.