Formulas and notation are based on the following 2-by-2 table cell labels:
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
p^1 = a / m1 (exposure proportion
in cases)
p^2 = c / m2 (exposure proportion
in controls)
o1^ = a / c (exposure odds in
cases)
o2^ = b / d (exposure odds in
controls)
OR^ = ad / bc (exposure odds ratio)
The above odds ratio represents an exposure odds ratio. The exposure odds ratio has the same interpretation as the disease odds ratio (e.g., an OR parameter of 1 indicates no association between the exposure and disease). Moreover, when the disease is rare (incidence < 5%), the odds ratio is approximately equal to the relative risk.