Hi, today i came across a weird problem. I found a panel data set online today with the number of cigarettes smoked for the period 2005-2010 and wanted to play around with it right away. I first estimated a model without fixed effects but with year dummies. As expected, one of the dummies was removed from the model (2005). Now I used the fixed effects estimator and observed something funny. Now, in addition to the 2005 dummy, the 2010 variable was also removed, as was the education variable. The education was removed because it is time invariant, but I can't explain the removal of 2010. I had initially concluded mulitcolinearity, but then the variable 1987 should have been removed in the first regression, right? Also the VIF values do not indicate a problem of mulitcolinearity (see picture). What could be the reason then? It must have something to do with the plm command, right?
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