Exact probabilities and confidence limits for binomial samples: applied to the difference between two proportions.

An exact probabilities method is proposed for computing the confidence limits of medical binomial parameters obtained based on the 2x2 contingency table. The developed algorithm was described and assessed for the difference between two binomial proportions (a bidimensional parameter). The behavior of the proposed method was analyzed and compared to four previously defined methods: Wald and Wilson, with and without continuity corrections. The exact probabilities method proved to be monotonic in computing the confidence limits. The experimental errors of the exact probabilities method applied to the difference between two proportions has never exceeded the imposed significance level of 5%.