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