The Minimally Meaningful Effect Size: A Vital Component of Pre-Registrations

Psychology is currently experiencing a replication crisis, wherein many attempts to replicate past studies have failed. Pre-registration is a valuable resource to enhance the replicability of research and maintain scientific rigour. However, the incorporation of information regarding effect size magnitude, namely the minimally meaningful effect size (MMES), has yet to be present within pre-registrations. Incorporating an MMES in pre-registrations encourages researchers to make a priori considerations regarding the minimum effect size threshold that must be met for a particular effect to be practically significant. This threshold depends on the research context, which includes study specific factors that interact with the effect size magnitude to determine the meaningfulness of an effect. Pre-registering the MMES will discourage researchers from haphazardly interpreting the magnitude of an effect (HIMEing; e.g., modifying post hoc what is considered meaningful), a behaviour that we deem a questionable research practice. Using a previously published study, we provide an example of how to incorporate the MMES into pre-registrations.