st: Re: messy ml problem

[Kit Baum <baum@bc.edu>]

Are you employing the trick that Stata uses to bound the correlation 
coefficient in the biprobit.ado code: estimate a bounded function of r, 
and then back-transform when the r is needed?

Kit Baum, Boston College Economics
http://ideas.repec.org/e/pba1.html

On Feb 5, 2005, at 2:33 AM, Jason wrote:


> I am using the function `binorm' to calcluate the density of the two
> binary variables. `binorm' takes three inputs, (conditional) means for 
> the
> two variables and a correlation coefficient (variances are normalized 
> to
> one).  Now there three arguments are, in my model, complicated 
> functions
> of elements from the 4 x 4 covariance matrix of the full system.
>
> The problem is Stata can't find any starting values for this procedure.
> I've looked at the correlation coefficient that is being generated and
> often it exceeds 1 or is smaller than -1, in which case binorm 
> produces on
> output.  I have tried imposing restrictions on various parameters when
> running `ml search' to see if I can get a correlation coefficient in 
> the
> unit interval, but that didn't work either.
>
> Any suggestions for how to proceed?
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