Testing whether treatment is 'better' than control with ordered categorical data: an evaluation of new methodology

A new test procedure is presented for the problem of testing whether a treatment is better than a control when there is ordered categorical data. The new test is based on the methodology developed for general 'one-sided' alternatives by Cohen and Sackrowitz. An evaluation of the test is made by comparing the power and expected p-values of the test with those of the Wilcoxon-Mann-Whitney test in examples. As predicted by the theoretical work by Cohen and Sackrowitz, the new test is seen to be preferable to the Wilcoxon-Mann-Whitney test. Computer programs to assist implementation of the new test are made available.