New subject: Way to Do Missing Value Imputation But Also Have Structurally Missing Data Unhampered?

14 Jul 2003

Thanks for the reply.  Indeed you are correct about the "are you pregnant"
analogy.  There is no sensible answer to those questions for those people.

Your solution to just impute everything, then know that particular cells is
intriguing.  On one hand, it is quite simple.  On the other hand, I was
under the impression that an iterative process went on behind the scenes in
estimating the missing values.  Your response leads me to believe that it is
iterative in the sense that it only uses information from data that exists
and does not substitute, then go through another iteration (think of a
cluster analysis procedure where people are first assigned, then can move
around a bit, depdenting upon what procedure you are using).

Once again, many thanks for getting back with me so quickly.

Zachary

-----Original Message-----
From: Gary King [mailto:king@harvard.edu]
Sent: Friday, July 11, 2003 9:14 PM
To: Feinstein, Zachary
Cc: Amelia Listserv
Subject: Re: Way to Do Missing Value Imputation But Also Have
Structurally Mis sing Data Unhampered?

a structural missing element would be the answer to the question "are you 
pregnant?" and the respondent is male.  you don't ask the question because 
there is no sensible random variable that this answer would produce.  if 
you havethis kind of problem, thenyou could merely impute this along 
with the rest but ignore the imputations for the structural zeros.

however, maybe what you have instead is just questions you decided not to 
ask some respondents for lack of time.  this is often called matrix 
sampling, and there's no problme both imputing and using theimputations 
from this setup.  in fact, since you determine the missingness pattern, 
you know that the asumptions of amelia apply (assuming you choose the 
respondents in a sensible way of course).

Gary

On Fri, 11 Jul 2003, Feinstein, Zachary wrote:

...
  I have a dataset of let's say 200 respondents by
10 variables.  This is for
...
  market research.  Occasionally people say Don't
Know or state they do not
 wish to respond to certain questions.  For the analyses I will be using the
...
  results for, I need to estimate the missing data here.
 A poor-person's way
...
  of doing it would be mean-substitution.

 Note that certain groups of people were not asked certain questions though
 based on skip patterns.  I cannot remove their column or row from the 200 X
...
  10 matrix and I still wish to figure what to do?

 Note that the scales are ordinal/continuous from 1 to 10.  I made it so that
...
  if they said Don't Know, the data becomes
missing.  I used zeroes to define
...
  the cells where it is structurally missing and quite
Kosher.  Perhaps I
 should use a character to make it explicit that it is not part of the scale
...
  in the future.

 Any help on how to use Amelia with this kind of situation is greatly valued
...
  and appreciated.  Thank you.

 --
 Zachary S. Feinstein
 Methodologist
 Harris Interactive
 zfeinstein(a)harrisinteractive.com
 http://www.harrisinteractive.com
 phone: (952) 541-7161

 435 Ford Road, Suite 250
 Minneapolis, MN  55426

RE: Way to Do Missing Value Imputation But Also Have Structurally Missing Data Unhampered?