A Sequential distribution-free two-sample grouped test with three possible decisions*

Summary A sequential two-sample grouped rank test with two possible decisions (onesided testing) developed by WILCOXON, RHODES and BRADLEY (1963) is generalized to a sequential test with three possible decisions (two-sided testing) using a method given by SOBEL and WALD (1949). An auxiliary table with some moments concerning LEHMANN'S alternatives for the normal distribution, is given in order to facilitate the choice of the alternative hypotheses.