Re: st: computing elasticities after using lpoly

[Nick Cox <njcoxstata@gmail.com>]

It seems to me that the whole point of -lpoly- is to be flexible about
modelling a relationship. It has absolutely no sense of any idea of an
overall slope. If you want a number for the slope, -lpoly- is useless.
If you want an independent view of how far the relationship after some
smoothing really is (e.g.) linear or monotonic, then -lpoly- can be
useful, mostly by providing a graph. For what you want, any
appropriate regression method will be better, such as -regress- or
-qreg-.

Nick

On Sat, Oct 6, 2012 at 10:06 AM, Arka Roy Chaudhuri <gabuisi@gmail.com> wrote:

> I am using Stata 11 on a Windows 7 machine. I am using lpoly to
> estimate nonparametric regressions of the form:
>
> log(y)=f(log(x)) + u
>
> where y= per capita expenditure on food
> x= total per capita expenditure
>
> Using lpoly, I can get a graph of per capita expenditure on food
> against total per capita expenditure. However I am also interested in
> obtaining expenditure elasticities of percapita expenditure on food at
> different levels of  total per capita expenditure i.e in my context
> d(log(y)/d(log(x)) where x and y are as earlier defined.The problem is
> that lpoly does not give estimates of any slope coefficients so I am
> at a loss on how to compute these elasticities. I would really
> appreciate if anybody could give me advice in this regard.
>
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