Confidence interval for a Cronbach reliability

Source: R/statpsych1.R

Computes a confidence interval for a population Cronbach reliability. The point estimate of Cronbach reliability assumes essentially tau-equivalent measurements and the confidence interval assumes parallel measurements.

ci.cronbach(alpha, rel, r, n)

Arguments

alpha

alpha level for 1-alpha confidence

rel

estimated Cronbach reliability

r

number of measurements (items, raters, etc.)

n

sample size

Value

Returns a 1-row matrix. The columns are:

  • Estimate - estimated Cronbach reliability (from input)

  • LL - lower limit of the confidence interval

  • UL - upper limit of the confidence interval

References

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 .

Examples

ci.cronbach(.05, .85, 7, 89)
#>  Estimate         SE        LL        UL
#>      0.85 0.02456518 0.7971254 0.8931436

# Should return:
# Estimate          SE        LL        UL
#     0.85  0.02456518 0.7971254 0.8931436