Effect Size Calculator

TATITIC CALCULATOR Effect Size A precise tool.
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What is the Effect Size & How does it work?

Effect size is a standardized metric that describes the magnitude of a difference between two groups, independent of sample size. Unlike p‑values, which only tell you whether an effect exists, effect size tells you how large that effect is, making it essential for meta‑analysis and power planning.

Cohen’s d is one of the most widely used effect‑size measures for comparing means. It expresses the difference between two group means in units of the pooled standard deviation, allowing researchers to compare results across studies with different scales.

d = \frac{\bar{X}_1 – \bar{X}_2}{s_{pooled}}
d = Cohen’s d (standardized mean difference)

Interpreting Cohen’s d follows conventional benchmarks: around 0.2 is considered a small effect, 0.5 a medium effect, and 0.8 or larger a large effect. However, context matters; in some fields even a d of 0.3 can be practically important.

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Frequently Asked Questions
What is Cohen's d?
Cohen's d is a measure that quantifies the difference between two group means in terms of standard deviation units.
How do I interpret Cohen's d values?
Typically, 0.2 is considered a small effect, 0.5 a medium effect, and 0.8 a large effect.
Can this calculator handle unequal sample sizes?
Yes, the calculator can compute Cohen's d for groups with different sample sizes.
What is the difference between effect size and p-value?
Effect size measures the magnitude of a difference, while a p-value indicates whether the observed difference is statistically significant.
Why is effect size important in research?
Effect size helps researchers understand the practical significance of their findings beyond statistical significance.
Can I use this calculator for non-normal data?
This calculator assumes normal distributions. For non-normal data, consider using alternative measures like Cohen's g or Hedges' g.
How do I calculate the pooled standard deviation?
The pooled standard deviation is calculated as the square root of the weighted average of the two group variances.

Results are for informational purposes only and do not constitute professional advice.