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 <[email protected]>:
> 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
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*
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