  The 'gold standard' design for three-arm trials refers to trials with an
active control and a placebo control in addition to the experimental treatment
group. This trial design is recommended when being ethically justifiable and it
allows the simultaneous comparison of experimental treatment, active control,
and placebo. Parametric testing methods have been studied plentifully over the
past years. However, these methods often tend to be liberal or conservative
when distributional assumptions are not met particularly with small sample
sizes. In this article, we introduce a studentized permutation test for testing
non-inferiority and superiority of the experimental treatment compared to the
active control in three-arm trials in the `gold standard' design. The
performance of the studentized permutation test for finite sample sizes is
assessed in a Monte-Carlo simulation study under various parameter
constellations. Emphasis is put on whether the studentized permutation test
meets the target significance level. For comparison purposes, commonly used
Wald-type tests are included in the simulation study. The simulation study
shows that the presented studentized permutation test for assessing
non-inferiority in three-arm trials in the 'gold standard' design outperforms
its competitors for count data. The methods discussed in this paper are
implemented in the R package ThreeArmedTrials which is available on the
comprehensive R archive network (CRAN).
