Univ. Grenoble Alpes, CNRS, LPNC (France) • Ghent University (Belgium)
How many participants/observations should I obtain for my next experiment, in order to show the effect I want to show ?
Usual algorithm (a priori NHST-PA): trying to guess the population effect size, plugging numbers (effect size and requested power) in the magic hat (the power function), and planning for a specific sample size.
But if I knew what (effect size) I am looking for, I would not bother making an experiment, right ?
Another approach consists in recruiting participants until we reach a predefined level of evidence. This is called sequential testing.
But this requires that we have a way to quantify evidence…
Example of the Sequential Bayes Factor procedure as presented in Schönbrodt, Wagenmakers, Zehetleitner, & Perugini (2017) and Schönbrodt & Wagenmakers (2017).