What does effect size indicate in research?

Effect size is a quantitative measure that indicates the magnitude of differences between groups or the strength of relationships within a study. It provides researchers with important information regarding the practical significance of their findings, beyond just whether the results are statistically significant.

While statistical significance tells us whether an observed effect is likely due to chance, effect size quantifies how large or meaningful that effect is in real-world terms. This helps in understanding the relevance and impact of the research findings. For example, even if a difference between two groups is statistically significant, a small effect size would suggest that the difference may not have practical implications. Conversely, a larger effect size indicates a more substantial difference or stronger relationship, which can influence decisions in clinical, educational, and policy contexts.

Other options, such as the duration of the study, the statistical significance of the results, or the number of participants involved, do not provide information on the magnitude or strength of the relationships being examined, which is why they do not capture the essence of what effect size conveys.