Hi Xiaobo, 

It's hard to know what is going on without seeing the original call to amelia, but I would definitely check that the variable is indeed numeric by using the following:

is.numeric(mydata[,13])

and check that amelia is also producing numerics:

is.numeric(a.out$imputation[[1]][,13])

What concerns me is that you say that the variable has character labels, which sounds more like a factor than a numeric. 

The error messages point to the variable having no non-missing observations. You can check how many observations are observed and missing using the following:

sum(!is.na(mydata[,13]))

If this is greater than zero, then there may be a problem with these functions. If so, please get in touch. 

Cheers,
matt.

On Thursday, September 8, 2011 at 1:59 PM, Xiaobo Lu wrote:

Dear all,

I am running into some problems with the newest version of Amelia II and
I cannot figure out exactly why, and I hope you can shed some lights on
these issues that I am running into.

I have successfully imputed 10 dataset by using Amelia II in R. The
imputed datasets look good, so is the overdispersed graph. However, when
I try to run "overimpute" and "compare.density" to conduct more
diagnostics for some specific variables, I am getting the following
error messages:

compare.density(a.out, var =13)
Error in density.default(vars[!is.na(vars)], na.rm = TRUE) :
argument 'x' must be numeric

overimpute(a.out, var =13)
Error in segments(xplot[ci.order], lowers[ci.order], xplot[ci.order], :
invalid first argument

I double-check and make sure variable 13 is indeed numeric, but they
have non-English labels.

I have used an older version of Amelia II and imputed a similar dataset
a couple years before, and I have no problem using these diagnostics
commands in R. Now that I have the most up-to-date version of Amelia II
on a new computer, I am running into these problems.

Any suggestions will be greatly appreciated. Thanks a lot in advance.


Best,
X

--
Xiaobo Lü
Assistant Professor
Bush School of Government and Public Service
Texas A&M University
Tel: (979) 845-6510
Fax: (979) 845-4155
Email: xlu@bushschool.tamu.edu
Website: http://www.xiaobolu.com
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