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st: RE: using egen, total() with weights

From   Nick Cox <>
To   "''" <>
Subject   st: RE: using egen, total() with weights
Date   Thu, 9 Feb 2012 23:00:37 +0000

I am a fan of -egen- when it's the right tool but I wouldn't start there at all. 

As you imply, -egen- can lose precision if you use the default variable type of -float-; the remedy is not to do that, but that's not the crux here. 

-total- offers direct support for pweights. I don't do -svy- but it sounds exactly the right place to start. 

Frankly, from your report you are getting some rather strange advice. 


Sheera Joy Olasky

I have a set of individual level survey data, which includes
person-weights. I would like to create population totals by year and
state. I am using Stata 11.2.

Originally I had thought to use bysort id: egen pop=total(weight)
where id is the state-year.

However, it was then suggested to me that I should be using sum
[aweight=weight]. This seems more complicated to me, since I'm not
sure how/if I could make new variables with the sum output in the same
way that I get a new variable with egen total (weights). Use of
scalars was recommended, but I have no experience with them.

Initially, when I compared the values I got with egen total(weight)
and sum [aweight=weight], they were very close--maybe off by about 4
people out of over 80,000,000. This imprecision is okay in this
scenario, but it got me concerned. I thought that perhaps there was
too much rounding happening with egen, so I generated the
total(weight) as double. The increased precision seems to have helped,
and now egen total(weight) and sum [aweight=weight] appear to give me
the same results when I spot check.

I don't feel completely confident, though. Before I go ahead and use
egen, I'd like to know if this is okay or ill-advised. I'd be curious
to know others' preferred way of handling this.

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