cocron (version 1.0-1)

cocron.two.coefficients: Statistical comparisons of two alpha coefficients

Description

Performs a test of significance for the difference between two alpha coefficients (Cronbach, 1951). The function expects alpha coefficients as input.

Usage

cocron.two.coefficients(alpha, n, dep = FALSE, r = NULL, los = 0.05, alternative = "two.sided")

Arguments

alpha

A numeric vector containing the two alpha coefficients.

n

A numeric vector containing the number of individuals who provided the data for the test for which alpha coefficients were determined.

dep

A logical indicating whether alpha coefficients are based on dependent groups of individuals (default is FALSE).

r

A single number specifying the correlation between the scores the alpha coefficients are based on. Only required if the alpha coefficients are computed for dependent groups of individuals (dep = TRUE).

los

A number indicating the level of significance (default is .05).

alternative

A character string specifying the alternative hypothesis; must be "two.sided" (default), "greater", or "less" (or just the initial letter).

Value

Returns an object of the class "cocron.two.coefficients" with the following slots:

alpha

Input parameter

n

Input parameter

dep

Input parameter

r

Input parameter

los

Input parameter

alternative

Input parameter

statistic

The value of the test statistic

distribution

The distribution of the test statistic

df

The degrees of freedom of the distribution of the test statistic

p.value

The p-value of the test

Details

For comparing two dependent or independent alpha coefficients (Cronbach, 1951), the methods described in Charter and Feldt (1996) are available, which were originally introduced in Feldt (1969) and Feldt (1980).

References

Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16, 297-334.

Charter, R. A., & Feldt, L. S. (1996). Testing the equality of two alpha coefficients. Perceptual and Motor Skills, 82, 763-768.

Feldt, L. S. (1969). A test of the hypothesis that Cronbach's alpha or Kuder-Richardson coefficient twenty is the same for two tests. Psychomelrika, 34, 363-373.

Feldt, L. S. (1980). A test of the hypothesis that Cronbach's alpha reliability coefficient is the same for two tests administered to the same sample. Psychometrika, 45, 99-105.

See Also

cocron, cocron.n.coefficients

Examples

# independent alpha coefficients
cocron.two.coefficients(alpha=c(.78,.71), n=c(41,151), dep=FALSE)

# dependent alpha coefficients
cocron.two.coefficients(alpha=c(.82,.89), n=27,dep=TRUE, r=.74)