Lay People Are Unimpressed by the Effect Sizes Typically Reported in Psychology

McPhetres, Jonathon, and Gordon Pennycook. 2020. “Lay People Are Unimpressed by the Effect Sizes Typically Reported in Psychological Science.” PsyArXiv. April 2. doi:10.31234/osf.io/qu9hn

Abstract: It is recommended that researchers report effect sizes along with statistical results to aid in interpreting the magnitude of results. According to recent surveys of published research, psychologists typically find effect sizes ranging from r = .11 to r = .30. While these numbers may be informative for scientists, no research has examined how lay people perceive the range of effect sizes typically reported in psychological research. In two studies, we showed online participants (N = 1,204) graphs depicting a range of effect sizes in different formats. We demonstrate that lay people perceive psychological effects to be small, rather meaningless, and unconvincing. Even the largest effects we examined (corresponding to a Cohen’s d = .90), which are exceedingly uncommon in reality, were considered small-to-moderate in size by lay people. Science communicators and policymakers should consider this obstacle when attempting to communicate the effectiveness of research results.