The Importance of Sample Size for Reproducibility of tDCS Effects

• Published in: Frontiers in human neuroscience 2016-09, Vol.10, p.453-453
• Main Authors: Minarik, Tamas, Berger, Barbara, Althaus, Laura, Bader, Veronika, Biebl, Bianca, Brotzeller, Franziska, Fusban, Theodor, Hegemann, Jessica, Jesteadt, Lea, Kalweit, Lukas, Leitner, Miriam, Linke, Francesca, Nabielska, Natalia, Reiter, Thomas, Schmitt, Daniela, Spraetz, Alexander, Sauseng, Paul
• Format: Article
• Language: English
• Subjects: Bias; Brain research; Cognition & reasoning; Cognitive ability; Collaboration; Cortex; Electrical stimulation of the brain; ESB; Excitability; Memory; Nervous system; Neuroscience; Neurosciences; Open access; Reintroduction; Reproducibility; Science; Studies
• ISSN: 1662-5161; 1662-5161
• DOI: 10.3389/fnhum.2016.00453

Introduction Cheap, easy to apply, well-tolerable, with the potential of altering cortical excitability, and for testing causalities—these are attributes that have made transcranial direct current stimulation (tDCS) a highly popular research tool in cognitive neuroscience. Since its reintroduction over 15 years ago by Nitsche and Paulus (2000), the number of publications reporting tDCS results has risen exponentially (a Scopus® literature search indicates over 500 such journal articles published in 2015 alone). [...]Cason and Medina (2016) find average statistical power in tDCS studies to be below 50%. [...]one potential reason for the reported inconsistencies might be that sample size is usually very small in most tDCS studies (including those from our research group). [...]depending on which studies are included in systematic reviews and meta- analyses (i.e., findings published in peer-reviewed journals; unpublished nil-effects; nil-effects reported as an additional finding in papers with the actual focus on another, significant, effect, etc.), small sample size in tDCS research could lead to both under—and overestimation of tDCS efficacy. By doing so, they overcome the problem of under-powering, an issue that seems so fundamental in tDCS research. [...]to investigate the effect of sample size on tDCS efficacy and to contribute to increased research transparency we designed a simple, pre-registered study (https://osf.io/eb9c5/?view_only=2743a0c4600943c998c2c37fbfb25846) with a sufficiently large number of young, healthy volunteers estimated with a priori power analysis.