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Re: st: pweight + aweight, double weights


From   Steve Samuels <sjsamuels@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: pweight + aweight, double weights
Date   Wed, 4 Aug 2010 17:14:05 -0400

I can see that the program is a little cryptic.  To clarify:

I applied- svy: ratio- to  R =  length_2/length_1  and got asymmetric
confidence intervals for R by computing them on the log scale and
transforming back.

The rate that Jochen asked for is rate =  (length_2 -
length_1)/length_1 = R - 1, and that is what the -antilog-- program
reports.  "relc" meant "relative change", which seemed clear to me, at
the time.

Steve

On Wed, Aug 4, 2010 at 1:37 PM, Steve Samuels <sjsamuels@gmail.com> wrote:
> Jochen--
> If you do a probability weighted mean of the  individual growth rates
> for a time period (single year, first year to last year) and weight by
> w =  (initial value) x (probability weight), you would wind up with
> the rate based on the probability-weighted aggregated sums. So Stas's
> solution is exactly the solution you seek. Moreover,  Stas's version
> will provide the correct standard error, one appropriate for a ratio
> estimate.
>
> You could also calculate the ratio estimate directly and get
> asymmetric CI's, which are likely to be more accurate than the
> symmetric intervals
>
> **************************CODE BEGINS**************************
> capture program drop _all
> program antilog
> local lparm  el(r(b),1,1)
> local se    sqrt(el(r(V),1,1))
> local bound  invttail(e(df_r),.025)*`se'
> local parm  exp(`lparm')
>
> local ll  exp(`lparm'  - `bound')
> local ul  exp( `lparm' + `bound')
> di  "relc = "  100*( `parm'-1)  "    ll = "  100*(`ll'-1)  "   ul = "
> 100*(`ul'-1)
> end
>
> sysuse auto, clear
> gen length_2 = displacement
> rename length length_1
> svyset _n
> svy: ratio length_2/length_1
> nlcom log(_b[_ratio_1])
> antilog
>
> ***************************CODE ENDS***************************
>
>
> Steve
> '
> Steven Samuels
> sjsamuels@gmail.com
> 18 Cantine's Island
> Saugerties NY 12477
> USA
> Voice: 845-246-0774
> Fax:    206-202-4783
>
>
>
> On Wed, Aug 4, 2010 at 11:43 AM, Stas Kolenikov <skolenik@gmail.com> wrote:
>> Who knows. You might be able to get identical answers, but you'll
>> spend more time trying to figure out the appropriate composition of
>> weights trying to reproduce the answer from those -total- commands.
>>
>> On Wed, Aug 4, 2010 at 2:58 AM, Jochen Späth <jochen.spaeth@iaw.edu> wrote:
>>> Hello Stas,
>>>
>>> thank you very much for your advice. I'm aware of the possibility of calculating the aggregate sums of investment for different subpopoluations using the pweight and calculating the aggregate (=aweighted) growth rates from the newly-generated data. I was just wondering whether there were a more "flexible" approach, such as, say multiplicating the two weight variables and use the result in a single -tabstat- or something like that.
>>
>> -
>
> On Tue, Aug 3, 2010 at 12:30 PM, Stas Kolenikov <skolenik@gmail.com> wrote:
>> You would probably want to
>>
>> svyset PSU [pw=your weight], strata(strata)
>> svy : total investment, over( year sector )
>> nlcom ([investment]_subpop_2 - [investment]_subpop_1)/[investment]_subpop_1
>>
>> or whatever labels the -total- command is going to give to individual
>> coefficients.
>>
>> On Tue, Aug 3, 2010 at 8:29 AM, Jochen Späth <jochen.spaeth@iaw.edu> wrote:
>>> Dear Statalisters,
>>>
>>> I have a question about weights, especially about "double weights".
>>>
>>> I have micro-data on firms containing information about their investment behaviour (amounts) for several years. I then went on to calculate the firms' individual (discrete) growth rates of investment, i.e.
>>>
>>> rate_t = (inv_t - inv_t-1) / inv_t-1
>>>
>>> and wish to use these individual growth rates to calculate average growth rates for, say, economic sectors. Thereby, I'd like to attach an aweight to the -tabstat-, -table- or other suitable command, such that firms with higher investments in t-1 contribute a higher share to the average growth rate. This is, of course, straightforward in Stata.
>>>
>>> However, since I have sampled data I need to attach to this operation also a pweight to get information for the population instead of the sample.
>>>
>>> Can I calculate the average growth rates from the individual ones or do I need to -collapse- or -table, replace- my data? It seems that -svyset- could be what I am looking for, but it seems rather complicated. Is there a way to avoid the -svyset- command and to go on with simple -tabstat- or alike instead?
>>>
>>> Best,
>>> Jochen
>>>
>



-- 
Steven Samuels
sjsamuels@gmail.com
18 Cantine's Island
Saugerties NY 12477
USA
Voice: 845-246-0774
Fax:    206-202-4783

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