Unconditional exact tests for the difference of binomial probabilities - contrasted and compared

Various exact tests for showing a di&erence between two treatments or the non-inferiority (therapeutic equivalence) based on the di&erence of two binomial proportions are compared. It is found that a frequently used test has to be applied with great caution due to its numerical instability. Furthermore, a test based on the score statistic can be recommended as a good compromise between a simple and powerful procedure. Finally, a likelihood ratio based exact test is introduced, which slightly outperforms all other tests from the literature with respect to power. The issue of sample size determination is brie;y addressed. All methods are illustrated with help of an example where two antihelmintic agents are compared. c © 2003 Elsevier B.V. All rights reserved.