Proposals for sample size calculation programs

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 Ill 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 Ill errors and the so-called q-volues, ii) minimum sample sizes required to keep the q-volues below pre-specified levels, and iii) detectable effect sizes of the so-called auxiliary alternatives. Conclusions: Proposals i and 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.