--- On Thu, 9/4/09, Juan Julio Gutierrez <[email protected]> wrote:
> I am using the polychroric command to calculate the
> correlation matrix of a set of 17 variables ( 8 binary 0-/1
> and 9 metric).
>
> After lenghty calculations STATA shows a matrix with
> missing values in the matrix, mostly between metric and
> binary variables. 4 metric variables have missing values
> correlations with binary variables.
>
> The results window show these messages. In red:
>
> could not calculate numerical derivatives
<snip>
As -polychoric- is not an official Stata command, please
report where you got it from.
The problem does not appear to be missing values but
that your model did not converge. Some things that might
cause this is when any of your binary variables have
very few ones or zeros, or when there are near perfect
dependencies between your variables.
Hope this helps,
Maarten
-----------------------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany
http://home.fsw.vu.nl/m.buis/
-----------------------------------------
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