# PSPP for Beginners: Cohen's d effect size for dependent-samples t-tests

For the paired-samples t-test, the comparisons are reflected in the difference scores. An example is that a participant in an experiment shows a change when before and after the experiment are compared.

Start by conducting the paired-samples t-test. The mean difference scores are shown in the descriptive statistics. Use these values in the calculator fields below. This example is from the paired-samples t-test.

Enter the mean of the difference scores (MD).
Enter the standard deviation of the difference scores (SDD).

*** Waiting for results ***

## Notes

The Cohen's d calculation for dependent-samples t tests are the difference score mean divided by the difference score standard deviation: MD / SDD.

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.

## Sources

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

Home | Start | Variables | Data | Descriptive | Relationship | Inferential | Effect size | Advanced | Video

This work is licensed under a Creative Commons Attribution 4.0 International License that allows sharing, adapting, and remixing.