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Re: st: Negative deff values in survey analysis


From   Stas Kolenikov <skolenik@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Negative deff values in survey analysis
Date   Wed, 3 Jun 2009 13:37:20 -0500

Your weights seem to be normalized per sample size, not the population
size. When you type -estat effects- in Stata 10 (are you using an
older version?), there's a warning about these scaling issues. Of
course it should not be producing negative DEFFs, so you would want to
contact tech-support@ ... unless Jeff Pitblado hasn't already
responded :))

2009/6/3 Ángel Rodríguez Laso <angelrlaso@gmail.com>:
> Dear Statalisters,
>
> I'm confused with the following results:
>
>
>
> . svyset psu [pweight=weight2007], strata(healtharea)fpc(psusperhealtharea)
>
>      pweight: weight2007
>          VCE: linearized
>     Strata 1: healtharea
>         SU 1: psu
>        FPC 1: psusperhealtharea
>
> .
> end of do-file
>
> . svy: tab p29, deff deft
> (running tabulate on estimation sample)
>
> Number of strata   =        11                  Number of obs      =     12140
> Number of PSUs     =      1266                  Population size    = 12134,139
>                                                Design df          =      1255
>
> -------------------------------------------------
> Any permanent
> disability | proportions         deff         deft
> ----------+--------------------------------------
>    0, no |       ,8887        -1981        ,9783
>    1, yes |       ,1113        -1981        ,9783
>          |
>    Total |           1
> -------------------------------------------------
>  Key:  proportions  =  cell proportions
>        deff         =  deff for variances of cell proportions
>        deft         =  deft for variances of cell proportions
>
>
>
>
> Why do I get large negative deff values? Deft resembles more what I
> was expecting, but it should be the square root of deff and obviously
> this is not the case. Do you have any explanation for these results?
>
> Many thanks,
>
> Angel Rodriguez-Laso
> *
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>



-- 
Stas Kolenikov, also found at http://stas.kolenikov.name
Small print: I use this email account for mailing lists only.

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