Time to Overcome the Neglect of Effect Sizes in Teaching Psychological Research Findings

Due to reliance on null-hypothesis significance testing, researchers had widely neglected effect size (ES) in their reporting of psychological research results. The American Psychological Association and others identified this as a problem and initiated reform, and ES reporting is now common in the scholarly literature. To what extent problematic ES neglect occurs in the teaching of psychological research findings remains unknown. In order to address this question, we analysed the content of 10 bestselling psychology textbooks from five popular sub-fields (Study 1). Overall, 76% (95% CI [69%, 79%]) of portrayals of empirical findings were devoid of useful ES information and merely mentioned the direction of the effect discussed. Such a direction-only description of any research finding would appear particularly uninformative if laypeople’s intuitions about the direction of this effect were already accurate. Study 2 therefore tested how well 286 non-psychology undergraduate students could guess the direction (or absence) of a representative sample of effects. Irrespective of psychological sub-field of the effects, average accuracy was only 47% [42%, 51%], demonstrating participants’ poor intuitions regarding these effects. This suggests that the predominant direction-only description of research findings in textbooks is not without merits. However, we argue that greater consideration of ES in the teaching of psychological research findings is desirable. We suggest three simple and efficient strategies to this end and weight their relative merits.