cronbach.alpha {cocron} | R Documentation |
Calculates Cronbach's alpha (Cronbach, 1951), a coefficient of internal consistency. The coefficient typically serves as an estimate of the reliability of a psychometric test.
cronbach.alpha(x, standardized = FALSE)
x |
A numeric data.frame/matrix with rows and columns corresponding to individuals and items, respectively. |
standardized |
A logic indicating whether a standardized Cronbach alpha should be calculated (default is FALSE). |
For a test consisting of k items that measures a quantity X, Cronbach's alpha is defined as
α = (k/k - 1)(1 - (∑_{i=1}^{k}{σ_Y}_i^2/σ_X^2))
with X = Y_1 + Y_2 + ... + Y_k. {σ_Y}_i^2 is the variance of item i, and σ_X^2 the variance of the total test score for a sample of individuals that completed the test.
The standardized Cronbach's alpha is defined as
α_s = (k\overline{r})/(1 + (k - 1)\overline{r})
where k is the number of items and \overline{r} the mean correlation between the items.
Cases that have missing values on any of the items are excluded.
Returns Cronbach's alpha as a numeric object.
Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16, 297-334.
cocron, cocron.n.coefficients, cocron.two.coefficients
data("knowledge") cronbach.alpha(knowledge$test1) cronbach.alpha(knowledge$test2)