The odds ratio is defined as the ratio of the odds of A in the presence of B and the odds of A in the presence of B.
The odds ratio can also be used to determine whether a particular exposure is a risk factor for a particular outcome, and to compare the magnitude of various risk factors for that outcome.
Formula to calculate odds ratio.
If 12 smokers have lung cancer, 60 smokers do not have lung cancer, 1 non-smoker has lung cancer, and 90 non-smokers do not have lung cancer, calculate the odd ratio.
Thus, the smokers has 20 times the odds of having lung cancer than non-smokers.