# Want an Effect Size (Cohen's d) Calculator in Excel?

## Go Deeper: 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?

Cohen's d values are calculated automatically in these t-Test templates:

1. Two-Sample Assuming Equal Variances
2. Two-Sample Assuming Unequal Variances
3. Paired Two Sample for Means

Find the templates by clicking on QI Macros > Stat Templates > F and t Tests: