Hi Marteen, I tried your example, it worked but once I went to my
exercise it says not concave and it does not work, even if I tried
different values.
also, I don't know what's wrong but one of my regression with biprobit
yesterday worked(i mean I have the output and the logfiles prooving
that it worked) and today it's giving me not concave.
grrr!!! (frustrated with the code not anyone:-)
Thanks in advance for your help.
Nirina
On 7/20/07, Maarten Buis <[email protected]> wrote:
--- Nirina F wrote:
> I know biprobit can just run but can anyone help if I would like to
> restrict rho to a value say 0.3
It is possible. You have to know that Stata doesn't maximize with
respect to rho, but to the Fisher's Z transformation of rho (also
known as the arc-hyperbolic tangent of rho, which is implemented
as the -atanh()- function in Stata). So if you want to constrain
the rho to be .3, than you have to tell Stata to constrain the
appropriate parameter to -atanh(.3)-. The appropriate parameter
is the constant in the athrho equation. This is what I have done
in the example below (except that I use -.3 instead of .3 as that
better fits in this data):
*----------- begin example -----------------
use http://www.stata-press.com/data/r9/school.dta, clear
local athrho = atanh(-.3)
constraint 1 [athrho]_cons = `athrho'
biprobit priv vote logptax loginc years, constraint(1)
*------------ end example ------------------
(For more on how to use examples I sent to the Statalist, see
http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )
Hope this helps,
Maarten
-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands
visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434
+31 20 5986715
http://home.fsw.vu.nl/m.buis/
-----------------------------------------
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