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Re: st: q-q plots, theoretical distribution with values higher than the sample's cutoff point


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: q-q plots, theoretical distribution with values higher than the sample's cutoff point
Date   Wed, 18 Jul 2012 17:48:37 +0100

These programs are in package -qpfit- on SSC.

The word "problem" here is ambiguous. My bias is to guess that your
data don't follow any of these distributions very well and the graphs
are telling you that. -su dec_ae, detail- would tell us a bit more.

Nick

On Wed, Jul 18, 2012 at 5:13 PM, Lucia Latino
<Latino@economia.uniroma2.it> wrote:

> I am having some problems with the q-q plots for Dagum, gb2, lognormal and
> Singh-Maddala distributions using programs written by Nick Cox.
>
> After having fit the distribution (e.g. lognfit dec_ae, svy), I run the
> command for the q-q plot (e.g. qlogn dec_ae [pweight=iwght]).
>
> I repeat the same procedure for the other distributions (Dagum, gb2 and
> Singh-Maddala). All the plots show a strange behavior: in all the qq-plots,
> the points follow a strongly nonlinear patters. At the beginning they follow
> the 45 degree line, then they depart significantly from the 45 degree line
> and become flat around the value 10,000, which is the max value for dec_ae.
>
> What does it mean? Why the theoretical distribution takes value higher than
> 10,000?
>
> I hope I was clear enough. I wish I could show you the plots, but I
> understood I cannot attach  them.
>
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