I see that constraints to produce valid imputations can be implemented in
the Gauss version of Amelia. However, Gauss is not available to me at this
time, and it may take me quite some time to figure out how implement the
constraints, since I've never used Gauss. In view of the circumstances I
want to make a request, hoping that I'm not stepping out of the boundaries
of the list. I wonder if somebody in the list would be willing to generate
the imputed data sets for a reasonable fee. I would provide the data,
imputation model, and the needed restrictions.
Thanks,
Leonelo E. Bautista, MD, DrPH
Assistant Professor
University of Wisconsin Medical School
Population Health Sciences
610 Walnut Street, 703 WARF
Madison, WI 53726-2397
Phone: (608)265-6176
Fax: (608)263-2820
-----Original Message-----
From: Gary King [mailto:king@harvard.edu]
Sent: Monday, June 07, 2004 3:01 PM
To: Leonelo Bautista
Cc: amelia(a)latte.harvard.edu
Subject: Re: [amelia] impossible values
Usually if you transform the data before Amelia, impute, and then
transform back, you can avoid this problem. See
http://gking.harvard.edu/amelia/node22.html for more details about this
and other procedures in more complicated situations.
Best of luck,
Gary King
: Gary King, King(a)Harvard.Edu
http://GKing.Harvard.Edu :
: Center for Basic Research Direct (617) 495-2027 :
: in the Social Sciences Assistant (617) 495-9271 :
: 34 Kirkland Street, Rm. 2 HU-MIT DC (617) 495-4734 :
: Harvard U, Cambridge, MA 02138 eFax (617) 812-8581 :
On Mon, 7 Jun 2004, Leonelo Bautista wrote:
I'm imputing values for missing blood lipids
(roughly 20% out of 3000
observations) in a cross-sectional data set. Some of the imputed values
are
not possible (for example, negative triglycerides
levels). I'm not sure
how
to handle these imputed values. Should I just ignore
then and go ahead
with
the analysis? Is it possible to impose restrictions on
the model (using
Amelia) to make all triglyceride values positive?
Any suggestions will be appreciated.
Leonelo E. Bautista, MD, DrPH
Assistant Professor
University of Wisconsin Medical School
Population Health Sciences
610 Walnut Street, 703 WARF
Madison, WI 53726-2397
Phone: (608)265-6176
Fax: (608)263-2820