What does effect size quantify?

Effect size quantifies the strength of a phenomenon or relationship, making it a crucial concept in statistical analysis. It provides a measure of the magnitude of the difference or association observed in a study, which allows researchers to understand not just whether an effect exists, but how substantial that effect is.

For example, in experiments or correlational studies, reporting effect sizes can help to determine whether the observed differences or relationships are not only statistically significant but also meaningful in practical terms. This is particularly important when considering how to interpret results and apply findings in real-world settings.

In contrast, the other options do not accurately capture what effect size represents. Variance refers to the spread or dispersion of data points in a dataset, not the strength of a relationship. Reliability pertains to the consistency of survey results, which is a different aspect of research methodology. The number of participants is related to study design but does not relate to the strength or size of an effect.