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My data is ordinal, and so missing values are imputed with the polr method from the MICE package. Now I have multiple datasets which I can run an Ordinal Logistic Regression on. But, as the title mentioned: I want to perform a Brant test to check the parallel regression assumption. How can I perform such a test on my imputed datasets?

olr <- with(imputed, polr(target ~ var1+var2)) 
olrsummary <- summary(pool(olr))

> brant(olr)
Error in formula.default(model) : invalid formula
> brant(olrsummary)
Error in temp.data[, name] : incorrect number of dimensions

I know I can take the first dataset with complete(imputed, 1) and use that for my Brant test. But that just don't sees right.

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Without a better description of the data you use, it is difficult to get an idea of what is causing your error. However, you can try the following:

  1. Verify that the target variable is an ordinal variable.
  2. Consider the possibility that you are using a buggy version of the brant package. I faced a similar problem running the function with my own dataset and surprisingly the problem disappeared when I forked the project and ran it as my own script.
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