A unified Stata package for calculating sample sizes for trials with binary outcomes (artbin)

Sample size calculation is essential in the design of a randomised clinical trial in order to ensure that there is adequate power to evaluate treatment. It is also used in the design of randomised experiments in other fields such as education, international development and social science. We describe the command artbin, to calculate sample size or power for a clinical trial or similar experiment with a binary outcome. A particular feature of artbin is that it can be used to design non-inferiority (NI) and substantial-superiority (SS) trials. Non-inferiority trials are used in the development of new treatment regimes, to test whether the experimental treatment is no worse than an existing treatment by more than a pre-specified amount. NI trials are used when the intervention is not expected to be superior, but has other benefits such as offering a shorter less complex regime that can reduce the risk of drug-resistant strains developing, of particular concern for countries without robust health care systems. We illustrate the command’s use in the STREAM trial, an NI design that demonstrated a shorter more intensive treatment for multi-drug resistant tuberculosis was only 1% less effective than the lengthier treatment recommended by the World Health Organisation. artbin also differs from the offical power command by allowing a wide range of statistical tests (score, Wald, conditional, trend across K groups), and offering calculations under local or distant alternatives, with or without continuity correction. artbin has been available since 2004 but recent updates include clearer syntax, clear documentation and some new features.