cronbach {psy}R Documentation

Cronbach's coefficient alpha

Description

Computes the Cronbach's reliability coefficient alpha. This coefficient may be applied to a series of items destinated to be aggregated in a single score. It estimates reliability in the framework of the domain sampling model.

Usage

cronbach(v1)

Arguments

v1 n*p matrix or dataframe, n subjects and p items

Details

Missing value are omitted in a "listwise" way (all items are removed even if only one of them is missing).

Value

A list with :

$sample.size Number of subjects under study
$number.of.items Number of items of the scale or questionnaire
$alpha alpha

Author(s)

Bruno Falissard

References

Nunnaly, J.C., Bernstein, I.H. (1994), Psychometric Theory, 3rd edition, McGraw-Hill Series in Psychology.

Examples

data(expsy)
cronbach(expsy[,1:10])  ## not good because item 2 is reversed (1 is high and 4 is low)
cronbach(cbind(expsy[,c(1,3:10)],-1*expsy[,2]))  ## better

datafile <- cbind(expsy[,c(1,3:10)],-1*expsy[,2])
library(boot)
cronbach.boot <- function(data,x) {cronbach(data[x,])[[3]]}
res <- boot(datafile,cronbach.boot,1000)
quantile(res$t,c(0.025,0.975))  ## two-sided bootstrapped confidence interval of Cronbach's alpha

[Package psy version 0.6 Index]