Effect Size Calculator (Cohen's d)
Calculate Cohen's d to measure the practical significance of an educational intervention or difference between two groups.
Cohen's d
0.543
Cohen's d vs Group 1 Mean
सूत्र
## 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.
हल किया गया उदाहरण
Treatment group scored mean 78 (SD = 10), control group scored mean 72 (SD = 12).
- 01Pooled SD = sqrt((100 + 144) / 2) = sqrt(122) = 11.05
- 02Mean difference: |78 - 72| = 6
- 03Cohen's d = 6 / 11.05 = 0.543
- 04Interpretation: Medium effect size
अक्सर पूछे जाने वाले प्रश्न
Why not just use p-values?
P-values indicate statistical significance but not practical importance. A large sample can make a tiny difference statistically significant.
What is a meaningful effect size in education?
Hattie suggests d = 0.4 as the threshold for a worthwhile intervention in education (the "hinge point").
Can effect size be negative?
This calculator reports the absolute value. A negative d would simply mean Group 2 scored higher than Group 1.