psychometric (version 2.2)

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)

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

Value

Returns a table with 3 elements

LCL

lower confidence limit of CI

ALPHA

coefficient alpha

UCL

upper confidence limit of CI

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)