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Re: st: using ML for hurdle model, invalid syntax error


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: using ML for hurdle model, invalid syntax error
Date   Fri, 22 Oct 2010 08:45:26 +0100 (BST)

--- On Thu, 21/10/10, Leny Mathew wrote:
> I'm trying to use the ml function to estimate a hurdle
> model. <snip>
> The code is below:
>
> ml model lf hurdle_gam (cnew= time tsq) (time tsq) if T
> <=3 & final==0, robust cluster(ID)
> ml check
<snip>
> args lnf beta1 beta2 lnphi
<snip>
> gen double `phi' = exp(`lnphi')
>                 =
> gen double __00000B = exp()
> invalid syntax

-ml- calls your evaluator (-hurdle_cam-) with first the name
of the variable in which to store the log-likelihood, than the
linear predictor of your first equation (-(cnew= time tsq)-),
than the linear predictor of the second equation (-(time tsq)-), 
and since you did not specify a third equation in your -ml model-
statement, there will be no third equation. So, even though you 
specified a third equation called lnphi in the -args- command, 
that local macro will be empty, so -exp(`lnphi')- will be 
evaluated as -exp()-, which gives your error. To solve this you 
need to specify the third equation in your -ml model statement. 
If you only want it to be a constant you can do that as follows:

ml model lf hurdle_gam (cnew= time tsq) (time tsq) /lnphi ///
   if T <=3 & final==0, robust cluster(ID)

Hope this helps,
Maarten

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://www.maartenbuis.nl
--------------------------


      

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