What does effect size measure in research?

Effect size is a quantitative measure that assesses the magnitude of the difference or relationship observed in research findings. It goes beyond merely indicating whether an effect exists (statistical significance) and offers a way to understand the practical importance of a result. For instance, in the context of an experiment, a large effect size suggests that the intervention or treatment has a considerable impact, which can be significant for real-world applications, such as policy development or clinical practices.

Understanding the practical significance of a result is crucial, especially in fields where the implications of research findings need to be translated into actions or interventions. For example, a statistically significant finding with a small effect size may not be meaningful in practice, while a large effect size, even if not statistically significant, could indicate a substantial impact worth considering. Thus, effect size is critical for interpreting the relevance of research outcomes in real-life scenarios.