CronbachAlpha: Cronbach's Coefficient Alpha
In AndriSignorell/DescTools: Tools for Descriptive Statistics

CronbachAlpha

R Documentation

Cronbach's Coefficient Alpha

Description

Cronbach's alpha is a measure of internal consistency and often used for validating psychometric tests. It determines the internal consistency or average correlation of items in a survey instrument to gauge its reliability. This reduces to Kuder-Richardson formula 20 (KR-20) when the columns of the data matrix are dichotomous.

Usage

CronbachAlpha(x, conf.level = NA, cond = FALSE, na.rm = FALSE)

Arguments

`x`	`n \times m` matrix or dataframe with item responses, k subjects (in rows) m items (in columns).
`conf.level`	confidence level of the interval. If set to `NA` (which is the default) no confidence interval will be calculated.
`cond`	logical. If set to `TRUE`, alpha is additionally calculated for the dataset with each item left out.
`na.rm`	logical, indicating whether `NA` values should be stripped before the computation proceeds. If set to `TRUE` only the complete cases of the ratings will be used. Defaults to `FALSE`.

Value

Either a numeric value or
a named vector of 3 columns if confidence levels are required (estimate, lower and upper ci) or

a list containing the following components, if the argument cond is set to TRUE:

`unconditional`	Cronbach's Alpha, either the single value only or with confidence intervals
`condCronbachAlpha`	The alpha that would be realized if the item were excluded

Author(s)

Andri Signorell <andri@signorell.net>, based on code of Harold C. Doran

References

Cohen, J. (1960), A coefficient of agreement for nominal scales. Educational and Psychological Measurement, 20, 37-46.

Examples

set.seed(1234)
tmp <- data.frame(
  item1=sample(c(0,1), 20, replace=TRUE),
  item2=sample(c(0,1), 20, replace=TRUE),
  item3=sample(c(0,1), 20, replace=TRUE),
  item4=sample(c(0,1), 20, replace=TRUE),
  item5=sample(c(0,1), 20, replace=TRUE)
  )

CronbachAlpha(tmp[,1:4], cond=FALSE, conf.level=0.95)
CronbachAlpha(tmp[,1:4], cond=TRUE, conf.level=0.95)

CronbachAlpha(tmp[,1:4], cond=FALSE)
CronbachAlpha(tmp[,1:2], cond=TRUE, conf.level=0.95)

## Not run: 
# Calculate bootstrap confidence intervals for CronbachAlpha
library(boot)
cronbach.boot <- function(data,x) {CronbachAlpha(data[x,])[[3]]}
res <- boot(datafile, cronbach.boot, 1000)
quantile(res$t, c(0.025,0.975))   # two-sided bootstrapped confidence interval of Cronbach's alpha
boot.ci(res, type="bca")          # adjusted bootstrap percentile (BCa) confidence interval (better)

## End(Not run)

AndriSignorell/DescTools documentation built on Nov. 11, 2024, 12:11 p.m.