alpha.CI: Confidence Interval for Coefficient Alpha

In psychometric: Applied Psychometric Theory

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

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)

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.

Note

Feldt et al., provide a number of procedures for making inferences about alpha (e.g., F test of the null hypothesis). Since the CI is the most versatile, it is the only function created in this package

Author(s)

Thomas D. Fletcher [e-mail]

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)

psychometric documentation built on Nov. 6, 2023, 1:06 a.m.