Hi William,
You do have a nested structure, so you'll have to decide which level is
interesting/feasible for imputation. The "cs" option, along with "intercs
=
TRUE" basically allows you to allow for different time trends within each
level of the cs variable. So, for you, that would either be at the
individual level or the neighborhood level. But intercs = TRUE increasing
the number of parameters quickly as the levels of the cs variable grow. So
you might have to rely on neighborhood trends, which is the way that you
have set it up.
There is no way to tell Amelia that certain variables are time-invariant.
You could use the transform() function after the imputation to impose this
restriction on the imputations, or just allow for the extra uncertainty
inherent in the imputation process and let it become part of the overall
uncertainty estimates that you get out of the Rubin rules.
Hope that helps!
Cheers,
Matt
~~~~~~~~~~~
Matthew Blackwell
Assistant Professor of Government
Harvard University
url:
http://www.mattblackwell.org
On Tue, Jul 21, 2015 at 2:00 PM William Johnston <wrj368(a)mail.harvard.edu>
wrote:
Hello,
I have a clustered longitudinal dataset consisting of four waves of data
on individuals who are nested in neighborhoods. I have missing data on
several time-varying variables at both the individual- and
neighborhood-levels. There are also some time-invariant individual
variables.
From what I gather in the documentation, I should do the following things
to account for this data structure:
-make sure the data is structured in long format, with a time indicator
and 4 rows for each individual.
-identify time series variable with ts = ____ option
-identify individual ID with idvars = ____ option
-identify neighborhood ID with cs = ____ option
-use to intercs = TRUE option to allow variation time trends
Here are my questions:
1. Am I specifying the cross section variable properly? Do I really have
two cross section variables (individual ID and neighborhood ID) or does the
idvars and ts options account for the clustering within person, over time?
2. How do I tell Amelia that some variables are time varying and some are
time invariant? Is there a way to have polytime=0 for some variables to
force a constant time trend, but then have polytime=1 for others?
Thanks,
-WRJ
--
William Johnston
Doctoral Candidate
Harvard Graduate School of Education
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