Should I remove this outlier? I am running a multiple variable regression predicting GDP per capita for U.S. states with a bunch of independent variables. Currently I have included the District of Columbia in the data set which has a much higher GDP per capita. Should I still include D.C. in the dataset?
My reasoning to include it is that D.C. has a higher population than states like Vermont, etc.

The criterion for making this decision should be based on
your purposes, and not influenced by the fact that the GDP per capita is for DC is about twice that of the leading state (NY) [which is in turn about twice that of the trailing state (MS)].
You say you are "... predicting DP per capita for U.S. states....$
If you consider DC as a 'state' for your purposes, then include CD for all useful independent variables. If you don't want to
predict GDP for DC, then what would be the motivation for including DC?
If you were trying to predict GDP for the US, then DC is part of the US and should be included. In that case you'd also have to decide
whether you consider various territories, etc. are "part of the US."
