It’s Not Effect Sizes So Much as Comments About Their Magnitude That Mislead Readers

ABSTRACT. The authors investigated the influence of effect size and comment inclusion on readers’ perceptions of research results. In three experiments, undergraduates, graduates, and facul’ty read a journal article that either included or did not include an effect size and commentary about the effect size. Contrary to a previous study by Robinson, Foulad, Williams, and Bera (2002), which concluded that including effect sizes causes readers to overestimate result importance, the authors found that including a comment about the magnitude of the effect size was more important than simply including the effect size in influencing undergraduates’ perceptions of research results’ inlportance. Graduate students and faculty members were less influenced by inclusion of either effect sizes or comments. Recommendations concerning effect size aad comment inclusion polices are discussed.