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st: polychoric matrix not positive definite


From   Tilahun <cherkos.z@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: polychoric matrix not positive definite
Date   Sun, 2 Dec 2012 01:39:25 +1100

Dear all,
while attempting to perform factor analysis on ordered varaiable (with
three categories), I had to compute polychoric correlation but stata
returned the matrix is 'not positive definitive'. When computing
tetrachoric correlation on binary data, and option  - , posdef - fixes the
problem and let the correlation computed. Is there any similar option that
I can use. Please advise.

The syntax are:

The option - posdef - below fixes the problem matrix 'not positive
definitive'

tetrachoric var1-var24, posdef
matrix rho = r(Rho)
factormat rho, pcf n(244)

But the syntax below returns matrix 'not positive definitive' and the
option - posdef- is not allowed here

polychoric var1-var24
matrix r=r(R)
factormat r, pcf n(244)

Your suggestion is much appreciated.

regards
Tilahun
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