What does "effect size" measure in research findings?

Effect size measures the magnitude of a relationship or difference identified in a study, providing a quantitative assessment of how significant that relationship or difference is in practical terms. This measurement goes beyond simply stating whether an effect is statistically significant; it informs researchers about the strength of that effect, which is crucial for understanding its real-world implications and relevance.

For instance, in the context of comparing two groups, a large effect size indicates a substantial difference between the groups, while a small effect size suggests that any observed difference may be less meaningful in a practical context. Effect sizes can be used in various statistical analyses, making them a pivotal component in interpreting research outcomes.

In contrast, the other choices focus on different aspects of research findings that do not pertain to measuring the strength of effects. Quantifying participant satisfaction is related to subjective experiences rather than statistical significance. The percentage of valid survey responses deals with data quality and integrity instead of the effect's magnitude. Finally, cost-effectiveness evaluates the efficiency of a research approach rather than the significance of the findings' effects. This distinction highlights the importance of effect size in the context of research validity and application.