Cronbach's alpha internal-consistency reliability

Computes Cronbach's alpha for a matrix or data frame of observed indicators: $$\alpha = \frac{k}{k - 1} \left(1 - \frac{\sum \sigma_i^2}{\sum \sum \sigma_{ij}}\right)$$

Usage

drm_cronbach_alpha(M)

Arguments

M

A numeric matrix or data frame of indicator columns.

Value

Numeric alpha scalar, or NA_real_ if \(k < 2\) or variance is non-positive.

References

Cronbach LJ (1951). “Coefficient Alpha and the Internal Structure of Tests.” Psychometrika, 16(3), 297–334. doi:10.1007/BF02310555 .