Proposals for sample size calculation programs.
OBJECTIVE
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 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.
Heinzl
H
H
Core Unit for Medical Statistics and Informatics, Medical University of Vienna, Vienna, Austria.
Benner
A
A
Ittrich
C
C
Mittlböck
M
M
D002986:Clinical Trials as Topic / Q000379:methods*; D003627:Data Interpretation, Statistical; D006801:Humans; D015233:Models, Statistical; D008962:Models, Theoretical; D018401:Sample Size; D012984:Software