alpha {psychometric}

Cronbach's Coefficient Alpha

Description

Coefficient alpha is a measure of internal consistency. It is a standard measure of reliability for tests.

Usage

alpha(x)

Arguments

x

Data.frame or matrix object with rows corresponding individuals and columns to items

Details

You can specify any portion of a matrix or data.frame. For instance, if using a data.frame with numerous variables corresponding to items, one can specify subsets of those items. See examples below.
alpha <- k/(k-1)*(1-SumSxi/Sx)
where k is the number of items, Sx is the standard deviaton of the total test, and SumSxi is the sum of the standard deviations for each item.

Value

coefficient alpha

Author(s)

Thomas D. Fletcher [e-mail]

References

Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 6, 297-334.

See Also

alpha.CI

Examples

data(attitude)
alpha(attitude)
alpha(attitude[,1:5])