Why, when, and how to (or not to) preregister a simulation study

Simulation studies play a central role in methodological research by providing evidence about the empirical performance of statistical methods. At the same time, they involve substantial researcher degrees of freedom in the choice of data-generating mechanisms, methods, performance measures, and reporting decisions, which can undermine the credibility of their results. Preregistration has been proposed as a tool to increase transparency and reduce such flexibility, yet its role in simulation studies remains contested. In this paper, we discuss why researchers should or should not preregister their simulation studies, elaborating on the theoretical and pragmatic benefits as well as disadvantages of preregistration. Drawing on philosophical accounts, we argue that preregistration primarily reduces epistemic uncertainty about which simulation conditions were considered and why, which enables honest evaluation of whether results support the conclusions drawn. We argue that the resulting benefits depend critically on the aims of a study and its position within the methodological research cycle. Late-phase studies that investigate mature methods tend to benefit more, while early-phase studies investigating newly proposed methods generally benefit less from preregistration. We further discuss practical challenges specific to simulation studies, including the timing of preregistration, the role of preliminary simulations, and safeguards against post hoc registration. Finally, we outline concrete guidance on how to preregister simulation studies and discuss Registered Reports as a particularly promising format. Overall, we argue for a nuanced, purpose-driven use of preregistration that supports rather than hinders methodological progress.