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Re: st: creating sample weights


From   "Janelle Knox" <babeerage@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: creating sample weights
Date   Sat, 11 Aug 2007 17:28:08 +0100

Thanks a lot Steve!  That is very helpful.  I am fairly new to Stata,
and the dataset didn't have a weight built in.  So I really appreciate
your advice.

Cheers,

Jane

On 8/10/07, Steven Joel Hirsch Samuels <sjhsamuels@earthlink.net> wrote:
> On Aug 10, 2007, at 10:53 AM, Janelle Knox wrote:
>
> > I am trying to create a sample weight for a dataset, which will
> > correct for variations in gender, age, etc from population means.
> > Does anyone know how to do this, or where I can find information for
> > setting up a sample weight.... pweight=?
> >
> > Thanks,
> > Jane
>
> Jane, you cannot do it to match population means.  However you can do
> it to match population percentages in different categories.  This
> technique for this  is known as "raking".  In Stata this is available
> in Nick Winter's program -survwgt rake-.  Type "ssc install
> survwgt".   By the way,  "pweight" is a stata reserved word.
>
>
> A good reference for practice is: http://www.abtassociates.com/
> presentations/raking_survey_data_2_JOS.pdf
>
> Warning: If you are not experienced with weighting, you can run into
> many problems. Raking will not fix, and might even worsen, certain
> kinds of sample deficiencies.  If you have followed recent
> discussions on Statalist, you will be aware that not everyone
> recommends weighting before doing regressions.
>
> You don't say if there is an existing "design weight".  If so, I
> assume that it's name is "old_wt".  Otherwise, define "old_wt=1"
> before running the survwgt program.
>
>
> 1. Create grouped versions of the variables you wish to match in your
> original data set.
>
> 2. Now create separate data sets for each characteristic that you
> wish to match, these will contain the adjusted totals for each
> characteristic  Suppose your sample size is n=1,252.  I will
> arbitrarily add or subtract 1 from the category numbered 1 for each
> characteristic to make sure your adjusted sample totals add up to the
> actual total. Below is an example for creating a data set
> "agedat.dta" which contains the age group totals.
>
> 3. Merge these into your original data. .
>
> 4. The rake instructions are then (for example):
>
> survwgt rake old_wt, by(race gender age_gp) totvars(race_tot
> gender_tot age_tot) generate(new_wt)
>
> 5. "new_wt" is your new weight variable. It will probably contain
> fractions, but these will not affect the regressions.
>
>
> -Steve
>
> /*CREATE AGE DATA SET WITH ADJUSTED TOTALS SO THAT SAMPLE & POP
> PERCENTS MATCH */
> local ssize=1252
> clear
>
> /* Gender Data Set: 1 10% 2 20% 3 50% 4 20% */
> input age_gp pop_pct
> 1 .1
> 2 .2
> 3 .5
> 4 .2
> end
> gen age_tot=`ssize'*pop_pct
> list
> table age_gp , c(sum age_tot) row
> sort age_tot
> save age_dat, replace
>
> /*****************CODE ENDS ***************************/
>
>
>
> Steven Joel Hirsch Samuels
>
> sjhsamuels@earthlink.net
> 18 Cantine's Island
> Saugerties, NY 12477
> Phone: 845-246-0774
> EFax: 208-498-7441
>
>
>
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