Using Anchor-Based Methods to Determine the Smallest Effect Size of Interest

Effect sizes are an important outcome of quantitative research, but few guidelines exist that explain how researchers can determine which effect sizes are meaningful. Psychologists often want to study effects that are large enough to make a difference to people’s subjective experience. Thus, subjective experience is one way to gauge meaningfulness of an effect. We illustrate how to quantify the minimum subjectively experienced difference—the smallest change in an outcome measure that individuals consider to be meaningful enough in their subjective experience such that they are willing to rate themselves as feeling different—using an anchor-based method with a global rating of change question applied to the positive and negative affect scale. For researchers interested in people’s subjective experiences, this anchor-based method provides one way to specify a smallest effect size of interest, which allows researchers to interpret observed results in terms of their theoretical and practical significance.