效应量计算器 — 公式

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

    • 计算示例

    A 20-item survey has an average inter-item correlation of 0.30.

    1. Numerator: 20 x 0.30 = 6.0
    2. Denominator: 1 + (20 - 1) x 0.30 = 1 + 5.7 = 6.7
    3. Alpha = 6.0 / 6.7 = 0.896
    4. Interpretation: Good reliability (0.80-0.89)