Re: st: Error in Poi's QUAIDS user-command

[Jorge Eduardo Pérez Pérez <jorge_perez@brown.edu>]

By the way, if the version is not the problem, consider moving this
thread to the Statalist forum

http://www.statalist.org/forums/

as this list is being deprecated soon and Mr. Poi may not get to read
the message.
--------------------------------------------
Jorge Eduardo Pérez Pérez
Graduate Student
Department of Economics
Brown University


On Fri, Apr 18, 2014 at 3:32 PM, Jorge Eduardo Pérez Pérez
<jorge_perez@brown.edu> wrote:
> Which version of -quaids- are you using? Mine is version 1.1.0 and the
> code reads:
>
> if (quadratics == "") {
> bofp = exp(lnp*beta')
> lnpindex = lnp*alpha' :+ st_numscalar("e(anot)")
> for(i=1; i<=rows(lnpindex); ++i) {
> lnpindex[i] = lnpindex[i] + 0.5*lnp[i,.]*gamma*lnp[i,.]'
> }
> }
>
>
> --------------------------------------------
> Jorge Eduardo Pérez Pérez
> Graduate Student
> Department of Economics
> Brown University
>
>
> On Fri, Apr 18, 2014 at 2:43 PM, Robin Winkler <robinwinkler@gmail.com> wrote:
>> Hi all,
>>
>> I believe I have found a serious error in the way in which the QUAIDS
>> user command written by Brian Poi computes elasticities.
>>
>> In the Mata code underlying the ado file - the relevant bit is pasted
>> below - the price index *lnpindex* used to compute the elasticities
>> does not include alpha 0, which is entered into the command suite as
>> *anot*. Hence, I have had the problem that  my price index was
>> underestimated, and the magnitude of the computed expenditure
>> elasticities tend to be way overstated.
>>
>> Should Mr Poi read this, I would be grateful for a comment.
>>
>> Robin
>>
>>
>>
>> *! version 1.0.0  29dec2011
>> /*
>> _quaids__utils.mata
>> Mata routines called by
>> nlsur__quaids.ado
>> quaids_estat.ado
>> quaids_p.ado
>> */
>>
>> mata
>>
>> mata set matastrict on
>>
>> void _quaids__expelas(string scalar touses,
>>      string scalar quadratics,
>>      string scalar atmeans,
>>      string scalar lnps,
>>      string scalar lnexps,
>>      real   scalar ndemo,
>>      string scalar demos,
>>      string scalar expelass)
>> {
>> real scalar i
>> real vector alpha, beta, lambda, rho
>> real vector bofp, cofp, lnpindex, lnexp, mbar
>> real matrix gamma, eta
>> real matrix shares, expelas, lnp, demo
>> alpha  = st_matrix("e(alpha)")
>> beta   = st_matrix("e(beta)")
>> gamma  = st_matrix("e(gamma)")
>> if (quadratics == "") {
>> lambda = st_matrix("e(lambda)")
>> }
>> else {
>> lambda = J(1, cols(beta), 0)
>> }
>> if (ndemo > 0) {
>> eta = st_matrix("e(eta)")
>> rho = st_matrix("e(rho)")
>> if (atmeans == "") {
>> st_view(demo=., ., demos, touses)
>> }
>> else {
>> demo = mean(st_data(., demos, touses))
>> }
>> }
>>
>> if (atmeans == "") {
>> st_view(shares=.,  ., st_global("e(lhs)"),  touses)
>> st_view(expelas=., ., expelass, touses)
>> st_view(lnp=.,     ., lnps, touses)
>> st_view(lnexp=.,   ., lnexps, touses)
>> }
>> else {
>> shares  = mean(st_data(., st_global("e(lhs)"), touses))
>> lnp     = mean(st_data(., lnps, touses))
>> lnexp   = mean(st_data(., lnexps, touses))
>> expelas = J(1, cols(shares), .)
>> }
>> if (quadratics == "") {
>> bofp = exp(lnp*beta')
>> lnpindex = lnp*alpha'
>> for(i=1; i<=rows(lnpindex); ++i) {
>> lnpindex[i] = lnpindex[i] + lnp[i,.]*gamma*lnp[i,.]'
>> }
>> }
>> else {
>> bofp = J(rows(lnp), 1, 1) // 1, so now div0 problem
>> lnpindex = J(rows(lnp), 1, 0)
>> }
>> if (ndemo > 0) {
>> cofp = J(rows(lnp), 1, 0)
>> for(i=1; i<=rows(lnp); ++i) {
>> cofp[i] = lnp[i,.]*(eta'*demo[i,.]')
>> }
>> cofp = exp(cofp)
>> mbar = 1 :+ demo*rho'
>> for(i=1; i<=rows(expelas); ++i) {
>> expelas[i,.] = 1 :+ 1:/shares[i,.]:*
>> (beta + demo[i,.]*eta + 2*lambda/bofp[i]/cofp[i]*
>> (lnexp[i]-ln(mbar[i])-lnpindex[i]))
>> }
>> }
>> else {
>> for(i=1; i<=rows(expelas); ++i) {
>> expelas[i,.] = 1 :+ 1:/shares[i,.]:*
>> (beta + 2*lambda/bofp[i]*(lnexp[i]-lnpindex[i]))
>> }
>> }
>> if (atmeans != "") {
>> st_matrix(expelass, expelas)
>> *
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