Effect Size Rechner (Cohen\ — Formel

How Cohen's d Measures Effect Size

Cohen's d quantifies the difference between two group means in standard deviation units, providing a measure of practical significance independent of sample size.

Formula

d = Mean_1 - Mean_2 / SD_pooled

Where SD_pooled = sqrt((SD_1^2 + SD_2^2) / 2)

Interpretation

  • Small effect: d = 0.2
  • Medium effect: d = 0.5
  • Large effect: d = 0.8

    • In education research, an effect size of 0.4 or higher is generally considered practically significant.

    Lösungsbeispiel

    Treatment group scored mean 78 (SD = 10), control group scored mean 72 (SD = 12).

    1. Pooled SD = sqrt((100 + 144) / 2) = sqrt(122) = 11.05
    2. Mean difference: |78 - 72| = 6
    3. Cohen's d = 6 / 11.05 = 0.543
    4. Interpretation: Medium effect size