cov.freqtab {equate} | R Documentation |
This function computes the covariance of a frequency table of class “freqtab
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cov.freqtab(x)
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)
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Returns the variance, in the univariate case, and the covariance for the bivariate
Anthony Albano tony.d.albano@gmail.com
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])