Calculateur de Taille d'Effet (Cohen) — Formule
## How Cronbach's Alpha Works
Cronbach's Alpha estimates reliability based on the number of items and their average correlation. Higher alpha means the items consistently measure the same construct.
### Standardized Alpha Formula
**Alpha = (k x r_avg) / (1 + (k - 1) x r_avg)**
Where k is the number of items and r_avg is the average inter-item correlation.
### Interpretation
- 0.90+: Excellent reliability
- 0.80-0.89: Good reliability
- 0.70-0.79: Acceptable reliability
- Below 0.70: Questionable to poor
Cronbach's Alpha estimates reliability based on the number of items and their average correlation. Higher alpha means the items consistently measure the same construct.
### Standardized Alpha Formula
**Alpha = (k x r_avg) / (1 + (k - 1) x r_avg)**
Where k is the number of items and r_avg is the average inter-item correlation.
### Interpretation
- 0.90+: Excellent reliability
- 0.80-0.89: Good reliability
- 0.70-0.79: Acceptable reliability
- Below 0.70: Questionable to poor
Exemple Résolu
A 20-item survey has an average inter-item correlation of 0.30.
- Numerator: 20 x 0.30 = 6.0
- Denominator: 1 + (20 - 1) x 0.30 = 1 + 5.7 = 6.7
- Alpha = 6.0 / 6.7 = 0.896
- Interpretation: Good reliability (0.80-0.89)