  The comparison of proportions is considered in the asymptotic generalized
linear model with the odds ratio as effect size. When several doses are
compared with a control assuming an order restriction, a Williams-type trend
test can be used. As an alternative, two variants of the closed testing
approach are considered, one using global Williams-tests in the partition
hypotheses, one with pairwise contrasts. Their advantages in terms of power and
simplicity are demonstrated. Related R-code is provided.
