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Hello,

I have a problem when i perform Hausman test. I do regression and i choose White diagonal or White period, i got N/A for some of my variables.
Please, see the attached file.
Can someone help me?
Thanks

As is well known, the Hausman test statistic is not guaranteed to have a computed covariance matrix that is positive semi-definite. Notably, it is computed as the difference of two matrices which is often negative definite, especially for small sample sizes.

The NAs are an indication that the corresponding diagonals of that covariance matrix are estimated to be negative.