Effect Size (Cohen's d) Calculator in Excel
What is Effect Size and Cohen's d?
Effect Size measures the relationship between two variables (how large an effect is). The larger the effect size, the stronger the relationship between two variables.
Cohen's d measures the DIFFERENCE between two variables' means divided by the Standard Deviation. If two groups have similar standard deviations and have the same group size, use Cohen's d. Note: It can only be used with normal data distributions.
Cohen's d Effect Size categorization:
d = 0.2 | SMALL (0.2 means the difference between the two groups' means is less than 0.2 Standard Deviations)
d = 0.3 - 0.5 | MEDIUM
d = 0.8 + | LARGE
NOTE: A d of 1 suggests the two groups differ by 1 Standard Deviation, while a d of 2 suggests 2 Standard Deviations, etc.
Where are these calculators located within QI Macros?
These values are calculated automatically and can be found in the following t-Test templates, located in the QI Macros > Stat Templates drop-down menu:
- Two-Sample Assuming Equal Variances
- Two-Sample Assuming Unequal Variances
- Paired Two Sample for Means
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