Hi Nicole, 

The singularity issue is often a result of linear combinations of variables, like a linear scaling of three variables. These are hard to detect with correlations. A better approach might be to add the variables in one at a time to see which one is the offender. One hack that might work is to run a regression of the first variable to be imputed on all of the other variables in the imputation model, then check to see if R drops any of the variables from the regression. That dropped variable is likely to be the culprit. 

Hope that helps!

Cheers,
matt.

~~~~~~~~~~~
Matthew Blackwell
Assistant Professor of Political Science
University of Rochester
url: http://www.mattblackwell.org


On Fri, Jul 5, 2013 at 3:50 PM, Nicole Janz <nicolejanz@gmail.com> wrote:
Dear all,

I am rerunning an imputation from a while ago (Amelia version 1.6.3.), and the only change is that I'm using a one year lag on all independent variables instead of the 'original' variables. Otherwise the code + data is pretty much the same, and it ran fine then. I now use Amelia_1.7.2.

After a chain length of 21, I get several lines saying error: inv(): matrix appears to be singular.

I have now already kicked out a variable that was .98 correlated with another one - that did not solve the problem.

The link to my data set: https://www.dropbox.com/s/uc2jst4asiwae4h/t1.Rdata

The Rcode: https://www.dropbox.com/s/33cfk7fqcasngdq/Janz_Darwin_0001.R

The session info is copied below.

I would be very grateful for any hints on what I can improve.

Thank you!
Nicole

--
> sessionInfo()
R version 3.0.1 (2013-05-16)
Platform: x86_64-apple-darwin10.8.0 (64-bit)

locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] Amelia_1.7.2            RcppArmadillo_0.3.900.0 Rcpp_0.10.3             foreign_0.8-54         

loaded via a namespace (and not attached):
[1] tools_3.0.1
--


Nicole Janz, PhD Cand.
Lecturer at Social Sciences Research Methods Centre
University of Cambridge
Department of Politics and International Studies
Skype: nicole.janz







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