Re: st: Code-problem - calculating demand elasticities with a QUAIDS

[Nick Cox <njcoxstata@gmail.com>]

I like the word "Doktorandin".

Stata's reference to

wmean

implies that the local macro i is undefined in the locale in which you
are working. From a glance at your code this is puzzling. Are you
defining all the code in the same locale, where locale means the same
interactive session OR program OR do-file OR do-file editor contents?

Note that "locale" is here my term borrowed from another language, and
not one that you will find in the Stata documentation.

I suggest it as a useful word: the locale of a local macro is the
space within which it is visible.

You can confirm what macros are visible at any point by peppering your code with

macro list

statements.
Nick
njcoxstata@gmail.com


On 22 November 2013 12:25,  <franziska.goetze@agroscope.admin.ch> wrote:
> Dear Statalist-Users
>
> I am trying to calculate budget and price elasticities for four meat products with a QUAIDS-model (using Swiss household data) (according to the method of Banks 1997 "Quadratic Engel Curves and Consumer Demand") and I have a problem with my code.
>
> This is (part of) the code I am using:
>
> quietly {
> foreach x of varlist w* lnp* lnx1_4 {
> sum `x'
> scalar `x'mean=r(mean)
> }
>
> * Price indexes
> global asum "_b[a1] * lnp1mean"
> forv i=2(1)4 {
> global asum "${asum} + _b[a`i'] * lnp`i'mean"
> }
> global gsum ""
> forv i=1(1)4 {
> forv j=1(1)4 {
> global gsum "${gsum} + 0.5 * _b[g`i'_`j'] * lnp`i'mean * lnp`j'mean"
> }
> }
> global lnaofp "5 + ${asum} ${gsum}" /* price index: ln a(p)*/
>
> global bofp "lnp1mean*_b[b1]"
> forv i=2(1)4 {
> global bofp "${bofp} + lnp`i'mean*_b[b`i']"
> }
> global bofp "(exp(${bofp}))" /* Cobb-Douglas price aggregator b(p) */
>
> * My's (i: delta budget share/delta ln-expenditure and ij: delta budget sh./delta ln-price)
> forv i=1(1)4 {
> global my`i' "_b[b`i'] + ((2*_b[l`i'])/${bofp})*(lnx1_4mean - (${lnaofp}))"
> }
> forv j=1(1)4 {
> global gsum2`j' ""
> forv k=1(1)4 {
> global gsum2`j' "${gsum2`j'} + _b[g`j'_`k'] * lnp`k'mean"
> }
> }
>
> forv i=1(1)4 {
> forv j=1(1)4 {
> global delta=cond(`i'==`j',1,0) /* Kronecker delta */
> global my`i'_`j' "_b[g`i'_`j'] - ${my`i'}*(_b[a`j']${gsum2`j'}) - ((_b[l`i']*_b[b`j'])/${bofp})*((lnx1_4mean - ${lnaofp})^2)"
> *}
> *}
>
> capture nlcom (elx`i': ${my`i'}/ w`i'mean + 1) (my`i'_`j':  ${my`i'_`j'}), post noheader
> if _rc {
> qui nlcom (elx`i': ${my`i'} / w`i'mean + 1) (my`i'_`j'f: (1e+2)*(${my`i'_`j'})), post noheader
> qui nlcom (elx`i': _b[elx`i']) (my`i'_`j':  _b[my`i'_`j'f]/(1e+2)), post noheader
> }
> }
> }
>
> * Uncompensated price elasticity
> nlcom (elx`i': _b[elx`i'])   (elu`i'_`j': _b[my`i'_`j']/ w`i'mean - ${delta}), post noheader
> * Compensated price elasticity
> nlcom (elc`i'_`j': _b[elu`i'_`j'] + _b[elx`i']* w`j'mean), noheader
> qui est restore quaidsc
>
> }
> end
>
> The problem seems to be in the "capture nlcom (elx`i': ${my`i'}/ w`i'mean + 1) ."-line (not sure), because Stata gives me the result:
>
> . do ""
>
> . nlcom (elx`i': ${my`i'}/ w`i'mean + 1) (my`i'_`j':  ${my`i'_`j'}), post noheader
> /wmean invalid name
> r(198);
>
> end of do-file
>
> r(198);
>
> I don't know, why it does not use the means of w1 to w4 (w1mean to w4mean) (w=budget share).
>
> It would be also interesting for me to know if there is another possibility to write the code for the calculation of "elx`i'".
>
> Thanks a lot,
> Franziska
>
>
> Franziska Götze, M. Sc.
> Doktorandin
>
> Eidgenössisches Departement für
> Wirtschaft, Bildung und Forschung WBF
> Forschungsanstalt Agroscope Reckenholz-Tänikon ART
> Sozioökonomie
>
> Tänikon, CH-8356 Ettenhausen
> Tel. +41 52 36 83225
> Fax +41 52 36 51190
> franziska.goetze@agroscope.admin.ch
> www.agroscope.ch
>
>
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