What is the term for the magnitude, or strength, of the relationship between two or more variables?

• A. Reliability
• B. Validity
• C. Effect size
• D. Power

Answer: (C)

The magnitude of the relationship between variables is described by the effect size. It tells you how strong the relationship or the size of the observed effect is, independent of how many participants you have. This helps you understand practical significance rather than just whether a relationship exists. For example, a correlation value indicates how tightly two variables move together, while differences in means between groups can be expressed as a standardized measure like Cohen’s d. Reliability and validity are about the quality of measurement—reliability asks whether a measure is consistent, validity asks whether it measures what it’s supposed to measure. Power is about the study’s ability to detect an effect if there is one, influenced by sample size, alpha, and the true effect size, not the strength of the relationship itself.