The binary data are often used in the medical field or in social sciences to study an effect between two groups. It can be for example the effect of a treatment between a treated and a control group. The outcome will be the number of successes and the total number of trials in each group. Let us call X1, X2 the successes and n1, n2 the number of trials, then X1 and X2 are binomial random variables with probabilities p1 and p2 respectively. The difference between these two probabilities will attest the difference of the effect between the two groups. Several statistics may be used to compare two probabilities.