psychometric (version 2.4)

alpha.CI: Confidence Interval for Coefficient Alpha

Description

Computes a one-tailed (or two-tailed) CI at the desired level for coefficient alpha

Usage

alpha.CI(alpha, k, N, level = 0.90, onesided = FALSE)

Value

Returns a table with 3 elements

LCL

lower confidence limit of CI

ALPHA

coefficient alpha

UCL

upper confidence limit of CI

Arguments

alpha

coefficient alpha to use for CI construction

k

number if items

N

sample size

level

Significance Level for constructing the CI, default is .90

onesided

return a one-sided (one-tailed) test, default is FALSE

Author

Thomas D. Fletcher

Warning

You must first compute alpha and then enter into function. alpha.CI will not evaluate a data.frame or matrix object.

Details

By inputting alpha, number of items and sample size, one can make inferences via a confidence interval. This can be used to compare two alpha coefficients (e.g., from two groups), or to compare alpha to some specified value (e.g., > = .7). onesided = FALSE renders a two-sided test (i.e., this is the difference between tails of .025/.975 and .05/.95)

References

Feldt, L. S., Woodruff, D. J., & Salih, F. A. (1987). Statistical inferences for coefficient alpha. Applied Psychological Measurement, 11, 93-103.

See Also

alpha

Examples

# From Feldt et al (1987)
# alpha = .79, #items = 26, #examinees = 41
# a two-tailed test 90% level

alpha.CI(.79, 26, 41)