Final answer:
Cohen's d measures effect size and the magnitude for small, medium, and large effects. A small effect size is around 0.2, a medium effect size is around 0.5, and a large effect size is around 0.8 according to Cohen's standards.
Step-by-step explanation:
Cohen's d is a measure of effect size based on the differences between two means, named after statistician Jacob Cohen. The magnitude of d for a small effect size is typically around 0.2, for a medium effect size it is around 0.5, and for a large effect size it is around 0.8. These values are based on Cohen's standards.