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Re: st: Quintiles


From   Austin Nichols <austinnichols@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Quintiles
Date   Thu, 9 Aug 2012 14:00:23 -0400

Leonardo Jaime Gonzalez Allende <leonardo.gonzalez@ine.cl>:
Try this example out:

sysuse auto, clear
keep price weight
ren price y
sort y
g s=sum(weight)
g c=(s)/(s[_N])
g qbreak=0
g w2=.
qui foreach l in 20 40 60 80 {
 replace qbreak=1 if c>=`l'/100 & c[_n-1]<`l'/100
 replace w2=s-(`l'/100*s[_N]) if c>=`l'/100 & c[_n-1]<`l'/100
 }
g w1=weight-w2
g id=_n
expand 2 if w2<.
g wt=weight
bys id: replace wt=w1 if _n==1 & w1<.
by id: replace wt=w2 if _n==2
g sum=sum(wt)
g cum=sum/sum[_N]
l if qb==1


On Wed, Aug 8, 2012 at 3:44 PM, Leonardo Jaime Gonzalez Allende
<leonardo.gonzalez@ine.cl> wrote:
> Yes, Maarten, you are right, sorry for writing you directly.
>
> I don't was planning to cut a person or household in many parts. The question was about a possible adjustment to the weight factor, if the observation of the sample is the cut point of the quintile.
>
> If I sort the households of a sample by their incomes, a household "x" could represents 300 households but the accumulated frequency of the population is e.g. 20,02%.
>
> My question was if there is an efficient way (command) to repeat the observation and adjust weight factor as follow:
>
> the same household "xa" now represents 280 households and now the accumulated frequency of the population is e.g. 20% (exactly) (leaving to the first quintile).
>
> the same household "xb" (the other part) represents 20 households accumulating a frequency of 20,02% of the population (changing to the second quintile this part).
>
> Regards,
>
> Leonardo
>
> -----Mensaje original-----
> De: Maarten Buis [mailto:maartenlbuis@gmail.com]
> Enviado el: Miércoles, 08 de Agosto de 2012 12:41
> Para: statalist@hsphsun2.harvard.edu
> Asunto: Re: st: Quintiles
>
> --- Leonardo Jaime Gonzalez Allende asked:
>>>> I'm trying to divide a sample of households (expanded)
>>>> into quintiles using the xtile command. I want to create
>>>> 5 groups with the exactly same quantity of population,
>>>> but using the xtitle command, the quantity of households
>>>> in each quintil is very slightly different to 20% when the
>>>> number of observations isn't exactly dividable by 5.
>>>> Do you know any command to divide the population
>>>> (sample expanded) into 5 groups of exactly same weight?
>
> --- I answered:
>>> That is logically impossible.
>
> -- Leonardo Jaime Gonzalez Allende wrote me privately:
>> sorry for write you directly, but I like to know, why is
>> logically impossible separate the population (by
>> incomes) in 5 groups of the same weith?
>
> Don't sent such follow-up questions privately. If you find my answer
> puzzling, than chances are that someone else who is following this
> discussion finds that too. This is explained in the Statalist FAQ.
>
> Think of it this way: How can you divide 6 persons in 5 equally sized
> groups? You could assign one person to each group, and than you are
> left with one person. If you could split the remaining 1 person up
> into 5 1/5th persons, than we could create 5 equally sized groups.
> However, that is impossible (or rather bloody, if we take that too
> literally). So given the inherently discrete nature of the number of
> observations you cannot divide your data up into 5 groups of exactly
> the same size if the number of observations in not dividable by 5.
>
> -- Maarten

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