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st: aweight


From   Rita Luk <Rita.Luk@camh.ca>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: aweight
Date   Mon, 29 Oct 2012 20:47:36 +0000

Hi Statalist,

Where can I find the computation detail of analytical weights (aweight) ?

In User guide 20.22.2, it says : If you specify aweights, they are: 1. Normalized to sum to N and then    2. Insert in the ... as fweights.

What does it mean (in formula) to normalize the weight to sum to N?  Where can I find the formula for the normalization.

I am working on point estimates of descriptive statisitcs (mean, median and histogram) using survey data and not concern about the variance at the moment. In particular, I want to  use non-svy commands with weights (let's leave the svy commands for now). I read comments from Steven Joel Hirsch Samuels and Austin Nichols and know that I will arrive at same weighted mean,median or histogram using either of the following 2 methods:
        
       Suppose I have a survey data set with sampling  weight variable wtpp (the sum of wtpp over the entire sample equals the total population of the target population)
1.  converted sampling wt to integer and use as freq weight:  gen double myfw=round(wtpp*100),  then tabstat xvar [fw=myfw], s(mean median)
2.  Use aweight :  tabstat xvar [aw=wtpp], s(mean median)

I know these methods give same estimates. But do why they give same estimates? Hence my question on the formula of normalization of weight given wtpp?

I appreciate if any one can help me on this.


Rita Luk|University of Toronto|33 Russell St. T5. Toronto,ON. M5S2S1. Canada|T: (416) 535-8501 x4727




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