Which of the following values indicates a very large effect size according to Cohen's d?

In the context of Cohen's d, effect size is a measure that expresses the magnitude of differences between groups in standardized terms. A very large effect size according to established conventions would typically be considered as a value significantly greater than 0.8.

While a Cohen's d value of 0.2 indicates a small effect and 0.5 indicates a medium effect, a value of 0.8 suggests a large effect. However, when examining values beyond this benchmark, a Cohen's d of 1.3 is indicative of a very large effect size. This value suggests that the difference between groups is substantial, providing strong evidence that the effect being measured has significant practical importance.

In research contexts, these distinctions are crucial since they help to understand not just whether an effect exists, but also how meaningful that effect is in real-world applications. By identifying a value like 1.3 as representative of a very large effect, practitioners can prioritize findings that promise robust interventions or substantive impact based on the studied effects.