Effect size

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Effect size for ANOVA

Partial Eta Squared

Trivial: <0.2 Small: 0.2-0.49 Moderate: 0.5-0.79 Large: >0.8  

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Knowing that the relationship is significant does not tell us whether this effect is strong or weak. So we need to calculate an effect size as well as the t-test.

Muijs, D. (2016).Doing Quantitative Research in Education With SPSS (2nd ed.). Sage Publications.


An effect size is a way to quantify the difference between two groups.

While a p-value can tell us whether or not there is a statistically significant difference between two groups, an effect size can tell us how large this difference actually is. In practice, effect sizes are much more interesting and useful to know than p-values.

Bobbit, Z. (2020, January 1). Effect Size: What It Is and Why It Matters. Statistics. Simplified. Statology. https://www.statology.org/effect-size/


contributed by Tania Nicole Sutherland

When the p-value is less than or equal to .05, this means there is a statistical significance. This is when we need to take effect size value into account. If the p-value is greater than .05, then there is no statistical difference so there would not be an effect size.

contributed by Lisa Daigle