reliability {CTT}R Documentation

Function for item reliability analysis

Description

This function performs reliability analyses, providing coefficient alpha and item statistics.

Usage

reliability(items, itemal = TRUE, NA.Delete = TRUE)

Arguments

items The scored response file with "0" (wrong) and "1" (correct) or Likert type data
itemal If itemal=FALSE (the default) no item analyses are conducted. If itemal=TRUE, the function will provide item means, item total correlations, and alpha if item is removed.
NA.Delete If NA.Delete=TRUE (the default) records are deleted listwise if there are missing responses. If NA.Delete=FALSE all NA values are changed to 0s.

Details

The input files must be scored files with "0" and "1" or numeric scales (e.g., Likert Type scales). Only basic scale information is returned to the screen. Use str() to view additional statistics that are available.

Value

number of items The number of items
number of persons The sample size used in calculating the values
alpha Crobach's alpha
scale.mean Average total sum socre
scale.sd Standard deviation of total sum score
alpha.if.deleted Cronbach's alpha if the corresponding item were deleted
pbis The item total correlation, with the item's contribution removed from the total
item.mean Average of each item

Author(s)

John T. Willse, Zhan Shu

References

Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometika, 16, 297-334.

See Also

score

Examples


# Scored input (data frame is preferred)
 x<-data.frame(matrix(c(0,0,0,0,0,
                        0,0,0,0,0,
                        0,0,0,0,1,
                        0,0,0,1,1,
                        0,0,1,1,1,
                        0,1,1,1,1,
                        1,1,1,1,1,
                        1,0,1,1,1,
                        0,0,0,1,1,
                        0,1,1,1,1),nrow=10,ncol=5,byrow=TRUE,
                        dimnames=list(c(paste("P",c(1:10),sep="")),c(paste("I",c(1:5),sep="")))))
reliability(x, itemal=TRUE)

# To see more item statisitics
str(reliability(x,itemal=TRUE))

[Package CTT version 1.0 Index]