[R] Polychoric and tetrachoric correlation

Andy Fugard a.fugard at ed.ac.uk
Mon Sep 1 19:25:54 CEST 2008

Hi there,

Am I correct to believe that tetrachoric correlation is a special case 
of polychoric correlation when there are only two levels to the ordered 
factor?  Thus it should be okay to use hetcor from the polycor package 
to build a matrix of correlations for binary variables?

If this is true, how can one estimate 95% confidence intervals for the 
correlations?  My guess would be

   mat = hetcor(dataframe)

   mat$correlation - (1.96 * mat$std.errors)
   mat$correlation + (1.96 * mat$std.errors)



Andy Fugard, Postgraduate Research Student
Psychology (Room S6), The University of Edinburgh,
   7 George Square, Edinburgh EH8 9JZ, UK
+44 (0)78 123 87190   http://figuraleffect.googlepages.com/

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