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Re: st: Multiple imputation showing missing values during imputation


From   "Michael I. Lichter" <mlichter@buffalo.edu>
To   Nailing Xia <nailingxia@gmail.com>
Subject   Re: st: Multiple imputation showing missing values during imputation
Date   Tue, 09 Dec 2008 17:42:26 -0500

Nailing,

Does -ice- provide information on each individual estimation? If so, you should check the -intreg- runs -- it may be that -intreg- is failing for some reason, possibly related to your interval() specifications, and that this is where the missing imputation data is coming from.

Michael

Nailing Xia wrote:
Thanks, Michael. I checked the lower bound and upper bound variables
as well as the interval variables for cases that Stata report imputed
values being missing, but didn't find anything that looks strange. As
a matter of fact, those cases are within an interval (i.e., both the
lower bound and upper bound variables have a valid but different
value, indicating that the interval variable should be imputed within
that range) that needs an imputation with -intreg-.

And here're the details of the dataset: I am using a longitudinal
dataset that follows over 10,000 children for several years. The
dataset has 5 waves, and in the model I included over 8,000
individuals. The -ice- command includes around 50 variables in
total--as some of the variables are time-specific but some are not,
the total number of variables are around 200. Options I used with
-ice- include "sub", "passive", "cmd", and "interval". For all imputed
variables (including categorical variables), I use -regress- (except
for those that are included in the "interval" option and thus use
-intreg-"). In "interval" option, I included 21 variables (out of over
200 variables included in -ice-), and 15 of them have the imputed
value missing problem as described earlier. The number of missing
cases range from 1 to 49. What happens is that Stata will replace the
missing cases with mean and continue imputing. Then at cycle 6 when it
is imputing one of the variable that has the imputed value missing
problem, Stata shows that "convergence not achieved" and stops
imputing (although I am not sure whether this problem relates to the
imputed value missing problem).

If you know anything about this problem, please help. Thanks a lot!

Nailing Xia


On Tue, Dec 9, 2008 at 3:23 PM, Michael I. Lichter <mlichter@buffalo.edu> wrote:
Nailing,

I suspect that you haven't gotten any responses because your question is (or
appears to be) very specific to your data, but you don't say much about the
specifics of your data. It might be helpful to describe the variables
involved and the constraints you are putting on the imputed data using the
-interval- option to -ice-.

Here's a stab in the dark, though. Is it possible that one or more of your
interval variables are missing for two cases in which your variable redlun5
is missing as well? If not, can you at least identify the two cases for
which -ice- is failing to make an imputation and see if there is anything
unusual about those cases' values on the other variables in the imputation?

-ml

Nailing Xia wrote:
Hi,

I am using -ice- for multiple imputation, and during the imputation
process, Stata shows that values for several imputed variables that
should have been imputed in previous cycle are actually missing. The
actual error message reads as: "I found that 2 missing value(s) of
redlun5 that should have been
imputed were missing at cycle 2. Replacing value(s) with mean, dumping
current data to file _ice_dump.dta and continuing."

Anyone knows what seems to cause this problem? By the way, this
problem did not exist when I imputed without using the -interval-
option. But I checked my code for -interval- option, and it seems
fine.

Many thanks!
Nailing Xia
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--
Michael I. Lichter, Ph.D.
Research Assistant Professor & NRSA Fellow
UB Department of Family Medicine / Primary Care Research Institute
UB Clinical Center, 462 Grider Street, Buffalo, NY 14215
Office: CC 125 / Phone: 716-898-4751 / E-Mail: mlichter@buffalo.edu

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--
Michael I. Lichter, Ph.D.
Research Assistant Professor & NRSA Fellow
UB Department of Family Medicine / Primary Care Research Institute
UB Clinical Center, 462 Grider Street, Buffalo, NY 14215
Office: CC 125 / Phone: 716-898-4751 / E-Mail: mlichter@buffalo.edu

*
*   For searches and help try:
*   http://www.stata.com/help.cgi?search
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



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