sirt (version 0.31-20)

stratified.cronbach.alpha: Stratified Cronbach's Alpha

Description

This function computes the stratified Cronbach's Alpha for composite scales (Cronbach, Schoenemann & McKie, 1965; Meyer, 2010).

Usage

stratified.cronbach.alpha(data, itemstrata)

Arguments

data

An $N$ times $I$ data frame

itemstrata

A matrix with two columns defining the item stratification. The first column contains the item names, the second column the item stratification label (these can be integers).

References

Cronbach, L.J., Schoenemann, P., & McKie, D. (1965). Alpha coefficient for stratified-parallel tests. Educational and Psychological Measurement, 25, 291-312. Meyer, P. (2010). Reliability. Cambridge: Oxford University Press.

Examples

data( data.read )
dat <- data.read
I <- ncol(dat)

# define item strata
itemstrata <- cbind( colnames(dat) , substring( colnames(dat) , 1 ,1 ) )
stratified.cronbach.alpha( data.read , itemstrata=itemstrata )
##   scale  I alpha mean.tot var.tot alpha.stratified
## 1 total 12 0.677    8.680   5.668            0.703
## 2     A  4 0.545    2.616   1.381               NA
## 3     B  4 0.381    2.811   1.059               NA
## 4     C  4 0.640    3.253   1.107               NA