alpha {epicalc}R Documentation

Cronbach's alpha

Description

Calculate reliability coefficient of items in a data frame

Usage

alpha (vars, dataFrame = .data, casewise = FALSE, reverse = TRUE, 
    decimal = 4, vars.to.reverse = NULL, var.labels = TRUE)   

Arguments

vars a vector containing at least three variables from the data frame
dataFrame data frame where items are set as variables
casewise whether on records with completed data on vars will be used
reverse whether item(s) negatively correlated with other majority will be reversed
decimal number of decimal places displayed
var.labels presence of descriptions of variables on the last column of output
vars.to.reverse variable(s) to reverse

Details

This function is based on the 'reliability' function from package 'Rcmdr', which computes Cronbach's alpha for a composite scale.

There must be at least three items in 'vars' specified by names of the variables or their index.

The argument 'reverse' (default = TRUE) automatically reverses items negatively correlated with other majority into negative and reports the activities in the first column of the last result section. This is however overwritten by the argument 'vars.to.reverse'

Similar to the 'reliability' function, users can see the effect of removing each item on the coefficents and the item-rest correlation.

Author(s)

Virasakdi Chongsuvivatwong <cvirasak@medicine.psu.ac.th>

See Also

'cronbach' from 'psy' package and 'reliability' from 'Rcmdr' package and 'tableStack' and 'unclassDataframe' of Epicalc

Examples

data(Cars93, package="MASS")
use(Cars93)
alpha(vars=c(Min.Price:MPG.highway, EngineSize))

data(Attitudes)
use(Attitudes)

## Please use full screen of Rconsole
## for better display of the labels.
alpha(qa1:qa18)
alpha(qa1:qa18, reverse=FALSE)


[Package epicalc version 2.6.0.5 Index]