Ladislas Nalborczyk

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).