psych (version 1.0-77)

polychor.matrix: Phi or Yule coefficient matrix to polychoric coefficient matrix

Description

Given a matrix of phi or Yule correlation coefficients and a vector of marginals, use John Fox's polycor function to convert these to polychoric correlations.

Some older correlation matrices were reported as matrices of Phi or of Yule correlations. That is, correlations were found from the two by two table of counts: lll{ a b c d } Yule Q is (ad - bc)/(ad+bc). With marginal frequencies of a+b, c+d, a+c, b+d.

Given a square matrix of such correlations, and the proportions for each variable that are in the a + b cells, it is possible to reconvert each correlation into a two by two table and then estimate the corresponding polychoric correlation (using John Fox's polychor function.

Usage

Yule2poly.matrix(x, v)
phi2poly.matrix(x, v)
Yule2phi.matrix(x, v)

Arguments

x

a matrix of phi or Yule coefficients

v

A vector of marginal frequencies

Value

• A matrix of correlations

Details

These functions call Yule2poly, Yule2phi or phi2poly for each cell of the matrix. See those functions for more details. See phi.demo for an example.

Examples

if(require(polycor)) {demo <- phi.demo() #compare the phi (lower off diagonal and polychoric correlations (upper off diagonal)
#show the result from poly.mat
round(demo$tetrachoric,2)
#show the result from phi2poly
#tetrachorics above the diagonal, phi below the diagonal 
round(demo$phis,2) }