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st: collapse with multiple sets of weights


From   "Dimitriy V. Masterov" <dvmaster@gmail.com>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   st: collapse with multiple sets of weights
Date   Thu, 12 Apr 2012 11:05:34 -0400

I am trying to aggregate some spatial data. Here's a simplified
version of my problem. I have two variables, average wage and
population, in three areas. I would like to sum the population, but
calculate a weighted mean of the average wage. Is there a way to do
this in one step using collapse?

For example, the following code gets the mean right, but the population "wrong":
set obs 3;
input
pop avgwage;
10	20;
20	10;
40	30;
egen double w=total(pop);
replace w=pop/w;
collapse (sum) pop (mean) avgwage [w=w];

I would like to see 70, not 90.

Is there a collapse-like command where I apply the weight only to the
mean calculation? I suppose I could do this in two collapse steps, but
that seems clunky.

DVM
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