DescTools (version 0.99.8.1)

CronbachAlpha: Cronbach's Coefficient Alpha

Description

Computes Cronbach's alpha. Cronbach's alpha determines the internal consistency or average correlation of items in a survey instrument to gauge its reliability. This reduces to KR-20 when the columns of the data matrix are dichotomous.

Usage

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

Arguments

x
A data frame or matrix with item responses.
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.

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:
  • unconditionalCronbach's Alpha, either the single value only or with confidence intervals
  • condCronbachAlphaThe alpha that would be realized if the item were excluded

References

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

See Also

CohenKappa, Kappam

Examples

Run this code
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)

# 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)

Run the code above in your browser using DataCamp Workspace