alpha.cronbach: Cronbach's alpha

In IRTpp: Estimating IRT Parameters using the IRT Methodology

Description

Cronbach's alpha measures how correlated are the items in a test

Usage

alpha.cronbach(test)

Arguments

test	a matrix or a Dataframe that holds the test response data

Details

the coefficient is calculated

α = (n/n-1)*(1 - (∑ V_i/V_t))

where $V_t$ is the variance of test scores and $V_i$ is the variance of item scores. It is desirable that the items are closely interrelated (coefficient near 1). This function was extracted from multilevel_2.5 package.

Value

Cronbach's alpha for the test and the number of individuals of test.

References

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

Examples

data <- simulateTest(model="2PL",items=10,individuals=1000)
alpha.cronbach(data$test)

IRTpp documentation built on May 29, 2017, 9:58 a.m.