Publicly Meaningful Law and Psychology Must Think Critically About Effect Sizes

Abstract

This comment examines a threat to the development of law and psychology as a “public science” (i.e., one that helps address important issues in society), a failure to think critically about effect sizes. As an applied field, law and psychology’s remit goes beyond exploring the theoretical relations between psychological constructs and behavior, to building knowledge about whether some observed relationship matters. Through three case studies, I suggest that those conducting law and psychology research and reporting it to legal actors should: (1) justify why effect sizes are meaningful and report them candidly and transparently, (2) scrutinize effect sizes to determine if they are plausible, and (3) plan studies such that they fit with the researchers’ inferential goals. I end with suggestions for implementing my recommendations, including a metaresearch agenda for law and psychology. Without these steps, law and psychology may mislead legal actors, such as judges and lawmakers, and will not live up to its promise as a public science.

Keywords: Law and psychology, public science, effect sizes, implicit bias, hungry judges, metaresearch, open science

JEL Classification: K10, K14