Understanding Effect Size in Research

Research Fundamentals #7

Effect size tells a researcher the magnitude of difference or relationship between multiple variables in a study. in a study, providing context beyond statistical significance. While p-values indicate statistical significance, the effect size is important because it tells us the strength of the actual relationship. therefore, has practical importance.
-Dr. Santangelo
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Effect Size Qualities

Small effect: A subtle but potentially meaningful difference.
Medium effect: A noticeable impact.
Large effect: A strong and substantial difference.

Conventional Measures of Effect Size

Pearson’s r (for correlation strength):
Small: 0.1
Medium: 0.3
Large: 0.5

Cohen’s d (for comparing two means):
Small: 0.2
Medium: 0.5
Large: 0.8

Eta-squared (η²) (for ANOVA effect size):
Small: 0.01
Medium: 0.06
Large: 0.14

Why Effect Size Matters

Practical Interpretation: Helps researchers assess whether findings are meaningful beyond mere significance.
Meta-Analysis: Allows for comparisons across studies. Study Design: Informs required sample size calculations.

Effect Size vs. Statistical Significance

A result can be statistically significant but have a small effect size, meaning it has little value or real-world impact. Conversely, a large effect size with an insignificant result may suggest an underpowered study.
– Dr. Santangelo
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Key Takeaways

Effect size measures the strength of an effect, not just its existence. Common metrics include Cohen’s d, Pearson’s r, and eta squared. Effect size provides context. Statistical significance alone is not enough Understanding effect size enhances the interpretation of research findings.

Critical Thinking Question

How does understanding effect size impact our ability to understand research?

Next Lesson: Practical vs. Statistical Significance

In the next lesson, we will explore the difference between practical and statistical significance, ensuring that research findings are not only mathematically valid but also meaningful in real-world applications.