cov.freqtab {equate}R Documentation

Covariance of a Frequency Table

Description

This function computes the covariance of a frequency table of class “freqtab

Usage

cov.freqtab(x)

Arguments

x score distribution of class “freqtab” for form X. Under the random groups design (i.e., no anchor test) x will contain the score scale in column 1, and the number of examinees obtaining each score in column 2. For the nonequivalent groups design a bivariate frequency table is used, where columns 1 and 2 include all score combinations for the total and anchor test score scales, and column 3 contains the number of examinees obtaining each combination (see freqtab for details)

Value

Returns the variance, in the univariate case, and the covariance for the bivariate

Author(s)

Anthony Albano tony.d.albano@gmail.com

See Also

freqtab, mean.freqtab

Examples

set.seed(2005)
x <- round(rnorm(1000,100,10))
xscale <- 70:130
xtab <- freqtab(x,xscale)
cov.freqtab(xtab); var(x)

yscale <- 0:36
vscale <- 0:12
ny <- freqtab(KBneat$y[,1],yscale,KBneat$y[,2],vscale)
cov.freqtab(ny); cov(KBneat$y[,1],KBneat$y[,2])

[Package equate version 0.1-1 Index]