Computes a confidence interval for a population Cronbach reliability. The point estimate of Cronbach's reliability assumes essentially tau-equivalent measurements and this confidence interval assumes parallel measurements.
ci.cronbach(alpha, rel, r, n)
alpha level for 1-alpha confidence
sample value of Cronbach's reliability
number of measurements (items, raters, etc.)
sample size
Returns a 1-row matrix. The columns are:
LL - lower limit of the confidence interval
UL - upper limit of the confidence interval
Feldt LS (1965). “The approximate sampling distribution of Kuder-Richardson reliability coefficient twenty.” Psychometrika, 30(3), 357--370. ISSN 0033-3123, doi:10.1007/BF02289499 .
ci.cronbach(.05, .85, 7, 89)
#> SE LL UL
#> [1,] 0.02456518 0.7971254 0.8931436
# Should return:
# SE LL UL
# [1,] 0.02456518 0.7971254 0.8931436