| stratified.cronbach.alpha {sirt} | R Documentation |
This function computes the stratified Cronbach's Alpha for composite scales (Cronbach, Schoenemann & McKie, 1965; Meyer, 2010).
stratified.cronbach.alpha(data, itemstrata=NULL)
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).
The default |
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.
############################################################################# # EXAMPLE 1: data.read ############################################################################# data( data.read ) dat <- data.read I <- ncol(dat) # apply function without defining item strata stratified.cronbach.alpha( data.read ) # 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 ## Not run: #************************** # reliability analysis in psych package library(psych) # Cronbach's alpha and item discriminations psych::alpha( dat ) # McDonald's omega psych::omega(dat, nfactors=1) # 1 factor ## Alpha: 0.69 ## Omega Total 0.69 ##=> Note that alpha in this function is the standardized Cronbach's ## alpha, i.e. alpha computed for standardized variables. psych::omega(dat, nfactors=2) # 2 factors ## Omega Total 0.72 psych::omega(dat, nfactors=3) # 3 factors ## Omega Total 0.74 ## End(Not run)