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Re: st: Restricted Ranges in Stata's Multiple Imputation Procedures


From   Maarten buis <maartenbuis@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Restricted Ranges in Stata's Multiple Imputation Procedures
Date   Mon, 19 Oct 2009 16:12:32 +0000 (GMT)

--- On Mon, 19/10/09, Hoogendoorn, Adriaan wrote:
> I created five imputed data files and noticed that in two
> of the imputed data sets, the imputed values for the
> variable of the follow-up study were severely out of the
> range of the observed cases (between 7 and 35) and in one
> imputed data set even way of the range of theoretically
> possible values (between 0 and 35). 
>  
> I would like to restrict the range of imputed values and
> tried the (predictive mean) matching option. This technique
> resulted into an imputed data set where the minimal
> observation was (value 7) was matched to nine of the
> fourteen missings. 

Hey Adriaan,

Given that the matching option stacks most observations at
the lowest value, I am guessing that it is mainly the lower
bound that bites. In that case you could try to predict that
values using -nbreg- rather than the default -regress-. 
Basically, you are tricking -ice- to see that variable as a
count rather than a continuous variable, so the lower bound 
of 0 will be automatically respected. The consequence is that
the imputed values will be integers and that no upper bound
is enforced.

*------------------ begin example ----------------------------
sysuse nlsw88, clear
// create some missing values
replace wage = . if runiform() < invlogit(-2 - union + south)

gen misswage = missing(wage)
ice wage union south grade, m(5) clear cmd(wage:nbreg)
stripplot wage if _mj > 0 , over(_mj) by(misswage) stack 
*------------------- end example -----------------------------
(For more on examples I sent to the Statalist see:
http://www.maartenbuis.nl/example_faq )

This example requires the -stripplot- package by Nick Cox, which
can be downloaded by typing in Stata: -ssc install stripplot-.

Hope this helps,
Maarten

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany

http://www.maartenbuis.nl
--------------------------

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