Effect Size Calculators

Introduction: The Effect Size Calculators provide a versatile tool for researchers and analysts engaged in comparative studies between two groups. This calculator incorporates two widely used effect size metrics, Cohen’s d and Hedge’s g, allowing users to gain insights into the standardized differences between group means.

Formula: The Effect Size (Cohen’s d) is calculated using the formula: Cohen’s d = |(M1 – M2)| / √((s1² + s2²) / 2), where M1 and M2 are the means, s1 and s2 are the standard deviations, and the pooled standard deviation is used. Hedge’s g is then computed by adjusting Cohen’s d for small sample sizes.

How to Use:

  1. Enter the mean, standard deviation, and sample size for both Group 1 and Group 2.
  2. Click the “Calculate” button to obtain both Cohen’s d and Hedge’s g.

Example: Consider Group 1 with a mean of 25, standard deviation of 5, and sample size of 30. Group 2 has a mean of 30, standard deviation of 8, and sample size of 35. Enter these values into the calculator and click “Calculate” to find Cohen’s d and Hedge’s g.


  1. What is Cohen’s d in effect size calculations?
    • Cohen’s d is a standardized metric that quantifies the difference between two means in terms of standard deviations.
  2. What is Hedge’s g and when is it used?
    • Hedge’s g is an adjustment to Cohen’s d for small sample sizes, providing a more accurate estimate of effect size.
  3. Can effect sizes be negative?
    • Yes, both Cohen’s d and Hedge’s g can be negative, indicating differences in the opposite direction.
  4. How is effect size interpreted?
    • A larger effect size indicates a more substantial difference between group means.
  5. Is a larger effect size always better?
    • The importance of effect size depends on the context of the study and the research question.
  6. When is Hedge’s g preferred over Cohen’s d?
    • Hedge’s g is recommended when dealing with small sample sizes to adjust for potential bias in Cohen’s d.
  7. What is a small, medium, and large effect size?
    • Interpretation varies, but generally, d around 0.2 is small, 0.5 is medium, and 0.8 or higher is large.
  8. How accurate are effect size calculations?
    • Accuracy depends on the quality and representativeness of the entered data.
  9. Is the calculator suitable for non-parametric data?
    • The calculator assumes normal distribution and may not be suitable for non-parametric data.
  10. Can I use this calculator for more than two groups?
    • No, this calculator is designed for two-group comparisons. For more than two, consider more specialized statistical methods.

Conclusion: In conclusion, the Effect Size Calculators offer a comprehensive solution for researchers seeking to quantify the differences between two groups. By providing both Cohen’s d and Hedge’s g, this tool enhances the interpretability of effect size metrics, allowing for a more nuanced analysis. Utilize this calculator to streamline your statistical calculations and gain meaningful insights from your comparative studies.

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