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Re: st: Spss's aggregate vs stata's collapse.


From   Amadou DIALLO <stata.diallo@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Spss's aggregate vs stata's collapse.
Date   Mon, 18 Apr 2011 17:02:16 +0300

I am still playing around with the weights but no results so far. Yes,
I need to match exactly spss' results. Can someone show where to find
spss' procedures manual?Best regards.
Bachir.

2011/4/13, Kaulisch, Marc <kaulisch@forschungsinfo.de>:
> Uli,
>
> SPSS looks inconsistent here. A look in the tutorial gives a clear insight
> in the mess:
> "SPSS automatically rounds weighted
> frequencies to the nearest integer. This rounding is done by default on the
> total weighted frequency,
> not on individual weights." (p. 15)
> "Rounding off these decimals is not an indifferent matter. Both 0.80 and
> 1.45 will be rounded to 1,
> which kills the very purpose of weighting. Suppose the weight of some cases
> is 0.30. If one case
> with weight 0.30 appears in a cell, the weighted (and rounded) total will be
> zero cases in that cell.
> If a second cell includes two cases from the same stratum, their weighted
> total will be 0.60,
> rounded to one case." (p.16)
>
> And in some procedures like CROSSTAB (Stata tab) you can turn off rounding
> the weights ;-)
>
> Really strange this...
>
> Marc
>
> -----Ursprüngliche Nachricht-----
> Von: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Ulrich Kohler
> Gesendet: Mittwoch, 13. April 2011 15:20
> An: statalist@hsphsun2.harvard.edu
> Betreff: Re: st: Spss's aggregate vs stata's collapse.
>
> Am Mittwoch, den 13.04.2011, 12:13 +0100 schrieb Brendan Halpin:
>> On Wed, Apr 13 2011, Amadou DIALLO wrote:
>>
>> > Brendan, Uli,
>> > Thanks for answers. Yes, it has to do with weights. Removing it
>> > yields same results. Apparently SPSS rounds non-integer weight to
>> > the nearest integer (the total weighted frequency, not individual
>> > weights (sic!):
>> > www.spsstools.net/Tutorials/WEIGHTING.pdf
>>
>> SPSS is doing the wrong thing here, then.
>>
>> > I've tried Brendan's solution but this is not working. So far, I
>> > can't duplicate results and am stuck. Will continue checking.
>>
>> If you really need to duplicate the results, you need to replicate
>> SPSS's "error". It may be enough to round the weight yourself.
>
> I know that this is not a SPSS list, however I'm still puzzled about what
> "rounding to the nearest integer" here really means. If a sampling weight
> has been rescaled such that the sum of weights is equal to the number of
> observations, there will be quite a number of weights below 0.5. Are they
> "rounded" to 0 then, meaning to drop them from the analysis? Or is zero not
> an integer value? Or do we use, the geometric mean or  harmonic mean between
> two subsequent numbers as the threshold for rounding, or what.
>
> SPSS = Some petty Statistical Software?
>
> Uli
>
>
>
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-- 

Amadou B. DIALLO, PhD.

Economist (Anti-Poverty Programs - DR Congo), AFTP3, The World Bank,
Washington DC.

Director, Center for Research and Training on Adult Health and Education.
Mayotte (FRANCE). www.aprosasoma.org

*
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