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# st: NLLS to GMM

 From penarol49 To statalist@hsphsun2.harvard.edu Subject st: NLLS to GMM Date Fri, 17 Feb 2012 19:40:43 -0800 (PST)

```Hi,

I had a question regarding how to define parameters using the interactive
GMM command, and I think the problem can be stated most simply by comparing
with the NLLS results.

I had one parameter I want to find (this is {kk1}) and one instrument. I can
do this easily with the nl command:

nl (V = {kk1}*ltfa + {c1}*(philag-{kk1}*ltfalag) +
{c2}*(philag-{kk1}*ltfalag)^2 + {c3}*(philag-{kk1}*ltfalag)^3),
variables(ltfa ltfalag philag) vce(cluster firmid)

This gives me what seems like the right solution for {kk1}. I am not looking
for the parameters in front of the (philag-{kk1}*ltfalag), but it seems
these have to be used in the nl syntax.

I then try to write this same thing by using gmm:

gmm (V - {kk1}*ltfa - {c1}*(philag-{kk1}*ltfalag) -
{c2}*(philag-{kk1}*ltfalag)^2 - {c3}*(philag-{kk1}*ltfalag)^3),
instruments(ltfa) vce(cluster firmid)

I cannot write it this way though, because it tells me that I have more
parameters than instruments (which is obviously true here, but it seems like
you have to put the parameters in front of any variable). And if I take
{c1},{c2}, and {c3} out then {kk1} is way too big.

Anyone know how I can do the same thing I am doing with nl using the gmm
command?

Thanks,
Ariel

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