grouping variable
Yi: outcome variable for observation number id
population in thousands
fraction black
fraction urban
fraction foreign born
surface rural road mileage/1000 pop
observation number
observation number for match
distance to match
Yi0: outcome control
Yi1: outcome treatment
matching variable: pop control
matching variable: black control
matching variable: urban control
matching variable: foreignb control
matching variable: sroadml control
matching variable: pop treatment
matching variable: black treatment
matching variable: urban treatment
matching variable: foreignb treatment
matching variable: sroadml treatment