Re: st: Multiple imputation: conditional option using categorical variables

[A Loumiotis <antonis.loumiotis@gmail.com>]

What exactly is the error that -ice- returns?  Could you please
specify the complete -ice- command that returns that error that you
mentioned?

Here is a nonsensical example that works.  In this example price is
only answered if categorical variable rep78 is not equal to 3.  Not
that I set price to missing whenever rep78 is missing and equal to
zero (pre-determined value) whenever rep78 is equal to 3.

*** Example starts
sysuse auto, clear
set seed 12345678
replace rep78=. if runiform()<.1
replace price=. if runiform()<.1
replace price=0 if rep78==3
replace price=. if rep78==.
ice m.rep78 price mpg, cond(price:inlist(rep78,1,2,4,5)) saving(catexam,replace)
use catexam, clear
sort _mi _mj
browse
*** Example ends

As you can see whenever rep78 is imputed to 3, -ice- automatically
assigns to price the pre-determined value of 0.

Going back to my November 2010 unanswered post about the conditional
option and categorical variables it is clear now to me that the first
specification is the appropriate one. Thanks for reminding me about
this post.  I will try to find it and bring a closure to it.

-ice- is a user written program that can be found at
http://www.ucl.ac.uk/~ucakjpr/.

Best,
Antonis

On Sat, Sep 28, 2013 at 1:29 PM, Hogerbrugge, M.J.A. (Martijn)
<M.J.A.Hogerbrugge@uu.nl> wrote:
> Dear Stata users,
>
> Does anybody know how to use the "conditional"-option for categorical variables in multiple imputation using ICE?
>
> The help file only provides an example using a dichotomous conditional variable ("female"). In that case, imputation on a particular variable is only performed if the condition is met (for instance "female == 1"). If the condition is false, a pre-determined value is imputed. To work correctly, the cases for which the condition is false need to have only one value on the variable that needs to be imputed. If more than one value is observed, ICE returns an error.
>
> In some instances, however, it is perfectly sensible to have multiple values in the variable to be imputed (for the observations for which the condition is false). Let me provide a quick example using the variable marital status:
> - the categories for marital status are [1] "married", [2] "divorced", and [3] "widowed"
> - marital status is observed at multiple time points
> - once a person is divorced or widowed, he or she remains so for the remainder of the observation points
> - the ICE command will look like this:
>
> .conditional(marstat_time2: if inlist(marstat_time1,1,.))
> .conditional(marstat_time3: if inlist(marstat_time2,1,.))
> .conditional(marstat_time4: if inlist(marstat_time3,1,.))
>
> and so on.
>
> Thus, marital status at a later time point is not imputed if the case was either divorced or widowed at the previous time point (i.e., not married [1] or missing [.]).
>
> Unfortunately, ICE returns an error for the reason described earlier. Is there some way to be able to do this kind of conditional imputation nonetheless? I tried looking for previous posts on a similar issue, and found one (http://www.stata.com/statalist/archive/2010-11/msg00708.html), but this post seems to be never been answered.
>
> BTW, I also looked into Stata's own imputation command (MI impute), but the conditional option is implimented in a similar way, and switching commands seems not to be a way to overcome this problem.
>
> Looking forward to your responses and help.
> ~Martijn Hogerbrugge
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