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Re: st: MI questions


From   "Christopher Parker" <parker@berkeley.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: MI questions
Date   Wed, 14 Feb 2007 06:34:38 -0800 (PST)

> Thanks, Marteen.

-- Christopher Parker <parker@berkeley.edu> wrote:
>> x1-x3 are not observed in dataset1, but I need them for theoretical
>> purposes. Therefore, I treat them as missing data in dataset1 and
>> impute them from dataset2 using demographic information common to
> both
>> datasets.
>>
>> Here's the problem: x1-x3, the imputed data, have negative values
>> after merging with dataset1. There shouldn't be negative values.
>> These are dichotomous 0-1 values when observed in dataset2.
>
> This seems to be a problem with Amelia II and not with Stata. I quick
> look at the documentation of Amelia II suggests that it primarily uses
> a multivariate normal to do the imputations. That is, your imputed
> values are drawn from a normal distribution thus explaining the
> negative values. However, all is not lost since the documentation also
> states that: "Amelia includes some limited capacity to deal directly
> with ordinal and nominal variables and to variables that require other
> transformations". And if that doesn't work you can always use -ice-,
> which is designed to deal with combinations of normal, dichotomous,
> ordinal, count, whatever data. Actually, I would do both and see if
> they both result in similar results, just to make sure that your
> outcomes aren't the result of some artifact of the algorithm.
>
> Hope this helps,
> Maarten
>
>
>
> -----------------------------------------
> Maarten L. Buis
> Department of Social Research Methodology
> Vrije Universiteit Amsterdam
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> 1081 HV Amsterdam
> The Netherlands
>
> visiting address:
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>
> http://home.fsw.vu.nl/m.buis/
> -----------------------------------------
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