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I'm using plm package to analyze unbalanced panel data. The problem is that some firms in the sample have only one year observation. This caused a problem whenever I use the following function (the purpose is to calculate white standard error):

vcovHC(pooling, method="white1", type="sss", cluster="group")

The error information is:

Error in crossprod(X, E(u, ul)) : non-conformable arguments

I'm pretty sure that this is caused by singletons in the data set. But the following call with a different argument causes no problem (the purpose is to calculate cluster robust standard error):

vcovHC(pooling, method="arellano", type="sss", cluster="group")

This works well.

I didn't find any solutions for this problem.

I wonder what's the proper method to analyze unbalanced panel data with singletons or whether I should drop those singletons.

If unbalanced panel data with singletons has no problem, then why does the vcovHC() function in plm package deal with this case with error?

Peter O.
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Gödel
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  • I'm voting to close this question as off-topic because it is about how to use R without a reproducible example. – gung - Reinstate Monica Mar 05 '16 at 10:45
  • Have a look if this answer (http://stackoverflow.com/a/31246351/4640346) helps with your problem as it seems to be related to linear dependence in your data (maybe after some data transformation for the FE model). – Helix123 Mar 06 '16 at 10:15
  • You could also try the latest development version as there was a bug fixed relating to the vcov framework in 1.5-13, see https://r-forge.r-project.org/R/?group_id=406 – Helix123 Mar 11 '16 at 08:31

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