# PSPP for Beginners: Cohen's d for independent-samples t-tests

## How to calculate Cohen's d for independent-samples t-tests

The strategy is to use the descriptive statistics from an independent-samples t-test output. Enter the appropriate values into the fields below. See the one-sample t-test page for a similar example.

This screenshot is an example from the independent-samples t-test output. The default calculator means have already been entered as default values in the data fields. Click on the button to get the Cohen's d value.

Enter the mean of group 1.
Enter the standard deviation of group 1.
Enter the mean of group 2.
Enter the standard deviation of group 2.

*** Waiting for results ***

## Notes

This version of Cohen's d is for independent-samples t tests. It uses pooled standard deviations.

Suggested effect size interpretation (Sawilowsky, 2009):

- .01: Very small
- .2: Small
- .5: Medium
- .8: Large
- 1.2: Very large
- 2.0: Huge

These value labels are not meant to be absolute standards. The interpretation depends upon the research context.

## References

Datanovia.com T-test Effect Size using Cohen's d Measure

Sawilowsky, S.S. (2009). New effect size rules of thumb. Journal of Modern Applied Statistical Methods. 8(2), 597-599. https://doi.org/10.22237/jmasm/1257035100

Wikipedia: Effect size

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