Summary
Objectives
: Numerous sample size calculation programs are available nowadays. They include both
commercial products as well as public domain and open source applications. We propose
modifications for these programs in order to even better support statistical consultation
during the planning stage of a two-armed clinical trial.
Methods
: Directional two-sided tests are commonly used for two-armed clinical trials. This
may lead to a non-negligible Type III error risk in a severely underpowered study.
In the case of a reasonably sized study the question for the so-called auxiliary alternative
may evolve.
Results
: We propose that sample size calculation programs should be able to compute i) Type
III errors and the so-called (q-values, ii) minimum sample sizes required to keep the (q-values below pre-specified levels, and iii) detectable effect sizes of the so-called
auxiliary alternatives.
Conclusions
: Proposals iand ii are intended to help prevent irresponsibly underpowered clinical
trials, whereas the proposal iii is meant as additional assistance for the planning
of reasonably sized clinical trials.
Keywords
Directional two-sided hypothesis test - Type III error - sample size calculation -
irresponsibly underpowered study - auxiliary alternative hypothesis
