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RE: st: egen "mean weight"


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: egen "mean weight"
Date   Sun, 4 Sep 2005 16:30:56 +0100

I don't know why -egenmore- is being singled
out here. The bigger issue is that -egen- 
does not take weights as such, so that 
use of -egen- with weights requires some 
work-around, for example the use of an 
option, as in -egen, xtile()- on -egenmore-. 
That creates an obligation to say which kinds of 
weights are supported. 

As far as -egenmore- is concerned, the whole 
package is pretty much an ad hoc accumulation of 
programs found to be needed by their authors. 
People should feel free to look at it and 
recognise oversights everywhere. Theme, 
direction and planning are non-existent. 

The original question was discussed in an 
FAQ a few years ago: 

FAQ     . . Calculating variables containing weighted group summary statistics
        . . . . . . . . . . . . . . . . . . . . .  N. J. Cox and S. P. Jenkins
        1/03    I want to calculate a variable containing weighted
                group summary statistics, but I do not want to
                collapse the data and egen does not support weights.
                How can I do this?
                http://www.stata.com/support/faqs/data/weighted.html

In that FAQ, we strongly commend the kind of
approach from first principles well explained 
here by Austin. 

Nick 
n.j.cox@durham.ac.uk 

austin nichols
 
> It seems to me an oversight that -ssc install egenmore- does not
> already give you this capability, especially since the xtile function
> in that package allows weights when dividing your sample into
> quantiles.  But it is easy enough, and good practice, to construct
> weighted means from first principles--you really never have to use
> egen, it's just a shortcut.
> . bys iid: gen double spop=sum(pop)
> . bys iid: replace spop=spop[_N]
> . gen double wtdwage=wage*pop/spop
> . bys iid: gen double meanwage=sum(wtdwage)
> . bys iid: replace meanwage=meanwage[_N]
> . drop spop wtdwage
> . compress meanwage
 
Jorge Tuesta 

> > Is it posible to create a average weight variable using "egen"?
> >  I normally write:
> >     egen mwage=mean(wage), by(iid)
> > but i would like "mean weight" (using [fweight=pop], for 
> example) not
> > simple mean. Is it posible?

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