Those data are also in the folder where migration process is estimated.

1) We take the last year for which the data is collected (2019). As there is no information on the number of citizens of the EU countires living in the EU,
Cyprus and Malta are eliminated from the sample. Luxembourg is eliminated as an outlier.
2) As there is no data of the citizens of: Estonia, Greece, Croatia, Latvia, Hungary, Austria, Slovenia, Slovakia  in Spain, we set their values to zero.
3) Due to availability of the data, the number of French citizens living in France is taken from 2016 
4) For the UK there is no data at all so we just subtract the number of immigrants from the EU countries from the population on 1 January 2019 (Eurostat data: DEMO_PJAN)