[R] Polychoric and tetrachoric correlation
a.fugard at ed.ac.uk
Wed Sep 3 11:52:41 CEST 2008
Yes, that's great - thanks!
John Fox wrote:
> Dear Andy,
> Yes, the tetrachoric correlation is a special case of the polychoric
> correlation when both factors are dichotomous.
> The 95-percent confidence interval that you suggest might be adequate if the
> sample size is sufficiently large and the correlation isn't too close to 0
> or 1, but it is probably not in general terribly trustworthy.
> I hope this helps,
> Original message:
> 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
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