11 Jul
2003
11 Jul
'03
10:14 p.m.
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