What is meant by effect size in experimental research?

Effect size refers to a quantitative measure that reflects the strength of the relationship or the magnitude of the difference between variables in experimental research. It provides insight into how substantial or impactful the results are, beyond just determining whether or not an effect exists. This measure can be crucial for understanding the practical significance of findings, as statistical significance alone does not convey how large or meaningful an effect is in a real-world context.

Effect size is particularly important because it allows researchers to compare the effectiveness of various interventions across different studies, regardless of the sample size. The other options, while relevant to research concepts, do not accurately encapsulate what effect size is. For instance, sample size relates to the number of participants in a study, statistical significance pertains to whether the results are due to chance, and qualitative assessments focus on descriptive and subjective evaluations, rather than quantitative measurements.