Re: st: Re: st. aweight

[Steve Samuels <sjsamuels@gmail.com>]

Two points:

1. In a well-designed probability sample, the sum of non-normalized
probability weights is an estimate of population
size. In the sampling literature, the standard symbol for
population size is "N", and the symbol for sample size is "n". So, Rita's
usage is correct.

2. -aweights- are _not_ restricted to integers.

See http://www.stata.com/statalist/archive/2004-11/msg00274.html for an
interesting thread about the relationship of analytic weights and
probability weights.


Steve

On Oct 29, 2012, at 6:15 PM, JVerkuilen (Gmail) wrote:

On Mon, Oct 29, 2012 at 5:44 PM, Rita Luk <Rita.Luk@camh.ca> wrote:
> 
> Hi Jverkulien,
> 
> I am slow to pick up what you say. For example my data has a sample size of only 5  obs, with the sanmpling wt variable wtpp:
> 
> caseid     wtpp
> 1.               60.74
> 2.     700.38
> 3.            139.64
> 4.    9671.57
> 5.    1545.32
> 
> Sum of wtpp= N= 12117.65
> 
> According to what you said, what does the analytical weight look like?   In addition to  being  normalized to sum to N, does the aweight need  to be integer?

In the case you discuss I think what would happen is that each of the
wtpp numbers would be divided by 12117.65 and then multiplied by 5.
The number you list as N is not N. N is 5.

Usually aweights are used when you have several means and their
sampling variances and want to generate an average mean weighted by
sampling variance. The sampling variances have each means N built in.
Hopefully if I'm wrong someone will chime in.
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