Sample size determination for BCI studies: how many subjects and trials?

Sample sizes and, consequently, statistical power have a large influence on the reliability of statistical results, but they are often neglected when planning and reporting studies of brain-computer interfaces (BCIs). This may be in part due to the limitations of classical power calculations, which do not apply to nested experimental designs, that are usually employed in BCI research. In this paper we introduce the methodology of simulation-based sample size determination (SSD) for the planning of BCI studies. We show how the proposed method can be used to determine the necessary number of subjects and trials to obtain a precise estimate of BCI accuracy, when the cost of sampling needs to be constrained by a budget. Furthermore, the method is fully general and can be applied in different experimental designs and in different statistical frameworks.