Hello, I am trying to run the maximum-likelihood estimation to estimate the inefficiency of health systems in Sub-Saharan African. I have some input variables and then some " exogenous determinant variables" that i would like to test. I am following the steps from "A Practitioner's Guide to Stochastic Frontier Analysis Using Stata". I am using the bc92 model of time decay (in)efficiency by Battese and Coelli (1992). But every time I try to run the actual model, I keep getting an error that my "exogenous variables" are not time-invariant within one or more of the cross-sections. I thought it was a good thing that my variables were not time-invariant, but now i am confused. Can someone explain the error and meaning? Any feedback would be helpful.
below is a sample of my data is attached.
below is a sample of my data is attached.
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