# Re: st: -nlcom- question

 From Ekrem Kalkan To statalist@hsphsun2.harvard.edu Subject Re: st: -nlcom- question Date Thu, 17 Dec 2009 21:56:46 +0200

```Hello,

you need to take a particular point of X , for example its mean or
minimum or maximum value.

You can do this:

sum X
gen xbar=r(mean)

and then insert "xbar" where it is needed in your nlcom formula

I hope this is what you asked.

Ekrem Kalkan

2009/12/16 Laurent Piet <Laurent.Piet@rennes.inra.fr>:
> Dear list,
>
> I think my problem can be solved with -nlcom- but I have not figured out how
> to do yet.
>
> I use the “function evaluator program” version of the -nl- command to fit a
> parametric Lorenz curve to observed data. The two parameters ‘a’ and ‘b’
> characterizing the functional form of the Lorenz curve are expressed as
> linear combinations of explanatory variables, say a = a0 + a1*X1 + a2*X2 and
> b = b0 + b1*X1 + b2*X2. So what I really get from -nl- are the a`i's and
> b`i's coefficients along with their associated std. err., t and p
> statistics.
>
> Now, I want to compute a third parameter, the Gini coefficient ‘g’, which is
> a non-linear combination of ‘a’ and ‘b’ involving the Beta function. What I
> ultimately want to compute are the g`i's, that is, the coefficients
> measuring the effects of the X`i's (including the constant) on ‘g’, with
> their associated std. err., t and p.
>
> I know how to use -nlcom- to do so when only the constant term is involved
> (nlcom g0: f(_b[/a0],_b[/b0])), but I couldn’t find how to deal with the
> explanatory variables X.
>
> Any idea would be welcome !
>
> Thanks in advance,
> Regards,
> Laurent
>
> --
> Laurent PIET
> ----------
> INRA, UMR1302 INRA-Agrocampus
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> ----------
> http://www.rennes.inra.fr/smart
>
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