Odds ratio is the ratio of the odds for the binary variable in two groups of the subjects, such as, males and females. If the two possible states of variable are labeled as 'success' and 'failure' then the odds ratio is the measure of the odds of a success in one group relative to that in the other group. When the odds of a success in each group are the same then the odds ratio is equal to one. It can be estimated as follows 
 


here a, b, c and d are the suitable frequencies in the two-by-two contingency table formed from data.