st: gmm moment evaluator program for system of equations

[Stefano Verde <verdes@tcd.ie>]

Dear statalisters,

I've estimated a QUAIDS model using -nlsur-. Now I want to test if
total expenditure is exogenous. So, I need to perform a Hausman type
test. I would say (but I might be wrong!) that the best way is to
estimate the system by -gmm-. Yet, this would require to write a
"moment evaluator program" which I'm not sure how should exactly be.

On the Stata help, I've found an example of moment evaluator program
for a single equation model (reported below). I'm not sure how I
should adapt it to the QUAIDS, which is a (nonlinear) system of
equations.

Any help would be greatly appreciated

Sincerely,
Stefano Verde

program gmm_ivreg
version 11
syntax varlist [if], at(name) rhs(varlist) depvar(varlist)
tempvar m
quietly gen double `m' = 0 `if'
local i 1
foreach var of varlist `rhs' {
quietly replace `m' = `m' + `var'*`at'[1,`i'] `if'
local `++i'
}
quietly replace `m' = `m' + `at'[1,`i'] `if'     // constant
quietly replace `varlist' = `depvar' - `m' `if'
end

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