What does the term effect size refer to?

Effect size is a crucial concept in research, particularly in psychology and other social sciences, that quantifies the size of an effect or the strength of a relationship between variables. It goes beyond mere significance testing, which indicates whether an effect exists, and provides information about how substantial that effect is. This measurement enables researchers to understand not just whether a result is statistically significant, but how meaningful or important that result may be in practical terms.

By providing a numerical value, effect size allows for comparisons across studies, facilitating meta-analyses and helping researchers to interpret the practical significance of their findings. A larger effect size implies a stronger relationship or a more substantial impact of an intervention, while a smaller effect size indicates a weaker association. This concept is vital when considering the implications of research findings in real-world applications.