How to Calculate Effect Size
What is Effect Size?
Effect size measures the practical significance of a result independent of sample size. A statistically significant result can have a trivially small effect size — effect size tells you whether it matters.
Step-by-Step Guide
- 1Cohen's d = (Mean₁ − Mean₂) / Pooled SD
- 2Small: d = 0.2; Medium: d = 0.5; Large: d = 0.8
- 3r = d / √(d² + 4) converts d to correlation
- 4η² (eta-squared) used for ANOVA effect size
Worked Examples
Frequently Asked Questions
What is Effect Size?
Effect size measures the practical significance of a result independent of sample size. A statistically significant result can have a trivially small effect size — effect size tells you whether it matters
How accurate is the Effect Size calculator?
The calculator uses the standard published formula for effect size. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.
What units does the Effect Size calculator use?
This calculator works with inches. You can enter values in the units shown — the calculator handles all conversions internally.
What formula does the Effect Size calculator use?
The calculator applies the standard formula for this type of calculation. See the 'How It Works' steps above for the detailed formula breakdown.
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