What is the main purpose of using effect size in psychological research?

The main purpose of using effect size in psychological research is to assess the strength of an experimental effect. Effect size provides a quantitative measure of the magnitude of the difference between groups or the strength of a relationship, independent of sample size. This is crucial because while statistical significance can indicate whether an effect exists, it does not convey how large or meaningful that effect is. By focusing on effect size, researchers can better understand the practical significance of their findings, allowing them to make more informed interpretations and decisions based on their data. For instance, knowing that a treatment has a small effect size can help clinicians and researchers determine if the intervention is worth implementing in a practical setting, as opposed to just knowing that the treatment was statistically significant.