mcron {CMO}R Documentation

Cronbach's Alpha

Description

Calculate Cronbach's Alpha

Usage

mcron(dataf, ifItemDel = TRUE, nBootRep = 0)

Arguments

dataf n*p data frame, n subjects p items
ifItemDel TRUE if Cronbach's alpha should be computed only from complete data sets (No NA allowed). FALSE otherwise.
nBootRep number of bootstrap replicates to estimate Cronbach's Alpha. If zero (default) no bootstrapping will be performed.

Details

Cronbach's alpha has an important use as a measure of the reliability of a psychometric instrument. It indicates the extent to which a set of test items can be treated as measuring a single latent variable. Alpha can take values between minus infinity and 1 (although only positive values make sense). As a rule of thumb, a proposed psychometric instrument should only be used if an alpha value of 0.70 or higher is obtained on a substantial sample. However the standard of reliability required varies between fields of psychology: cognitive tests (tests of intelligence or achievement) tend to be more reliable than tests of attitudes or personality. There is also variation within fields: it is easier to construct a reliable test of a specific attitude than of a general one, for example.

Value

AllAlpha Cronbach's alpha
IfItemDel
Item
number of items
Trennschaerfe
confidence measure
Alpha wenn geloescht
Cronbach's alpha if NA's are not allowed
Nalpha number of subjects
Boot.StatDist (only if bootstrapping is used) Distance statistic for Cronbach's Alpha
Boot.95PercConf (only if bootstrapping is used) 95% confidence interval for bootstrapping distance statistic
Boot.nBootRep (only if bootstrapping is used) number of bootstrap replicates used

Author(s)

Christian Montel

References

Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16, 297-333.

Allen, M.J., & Yen, W. M. (2002). Introduction to Measurement Theory. Long Grove, IL: Waveland Press.

See Also

function cronbach in package psy

Examples

#create some arbitrary results
data <- matrix(ceiling(runif(400)*100),nrow=20)
#works
#create some missing values does not work a BUG!
#data[round(runif(400)*0.7) == 1] <- NA
mcron(data,ifItemDel = TRUE,nBootRep=100)

[Package CMO version 1.02 Index]